Last year: 4th in South Group, winners
Captain: Simon Harmer
Coach: Anthony McGrath
In a nutshell: Snuck up on the blindside to win their maiden title last year after two wins in their first ten scheduled games, with skipper Harmer the star on Finals Day and Ravi Bopara - in his last season at the club - shining as a finisher despite his frustrations about his role. Bopara will be a big miss this year, but they still have the tools to make hay at Chelmsford.
Star: While not an official overseas player thanks to his UK ancestry visa, Cameron Delport brings a wealth of franchise experience at the top of the order. His innings against Surrey - 129 off 49 balls - was the most remarkable of last year's Blast, and his ability to score quickly and consistently against both spin and pace makes him key.
One to watch: Dan Lawrence was due a breakout summer but circumstances have transpired against him and he is yet to make the England debut that seemed inevitable. He is a star in T20, playing in "ultra-aggressive" fashion and striking at 163 against spinners over the last three years.
Verdict: Too reliant on batting to repeat last year's success, but quarters on the cards
Last year: 7th in South Group
Captain: James Vince/Sam Northeast
Coach: Adi Birrell
In a nutshell: Would have reached knockouts with victory against winless Glamorgan in final group game last year but somehow let Essex sneak through instead. Significantly weakened due to injury and unavailability this season: Liam Dawson is out for the season and Aneurin Donald is unlikely to feature; James Vince's wife is expecting her second child; Kyle Abbott, Fidel Edwards and Rilee Rossouw are stuck overseas. Discussions are ongoing with Shaheen Afridi about the possibility of staying on after Pakistan's England tour, who would be a trump card if available.
Star: After missing the 2018 tournament through injury, Mason Crane returned to T20 cricket with 11 wickets and an economy rate of 7.03 last season. With the Ageas Bowl generally spin-friendly and Hampshire playing five of their last six group games at home, he will be particularly crucial in the second half of the tournament.
One to watch: Scotland opener George Munsey is one of the top short-form batsmen in the associate world, and is a smart pick-up given his ability against spin, against which he strikes at 169 since 2018. Watch out in particular for his signature switch-hits and strong wrists, with clear evidence of his days playing hockey in his youth.
Verdict: Missing too many stars to have any real hope of reaching knockouts
Last year: 5th in South Group
Captain: Sam Billings
Coach: Matt Walker
In a nutshell: Somehow screwed up qualifications after six wins from first seven fixtures last summer, with three batting implosions in run chases and two abandonments in the final five leaving them a point short of Essex. Likely to be hampered by England call-ups for Billings and Joe Denly, but plenty of talent regardless.
Star: It has been a frustrating summer for Alex Blake - known affectionately as 'the Blake-cano' for his ability to erupt at the back end of an innings - after his decision to sign a white-ball contract has left him twiddling his thumbs. Faded after a bright start last year, but his finishing abilities will still be crucial.
One to watch: Left-arm spinner Imran Qayyum was vital last year, plugging away in the middle overs to finish with an economy rate of 7.50 and 12 wickets to his name. In an attack significantly weakened by the absences of Hardus Viljoen, Mohammad Nabi and Adam Milne, he will be the linchpin.
Verdict: Attack lacks bite but quarter-finals not beyond them
Last year: 3rd in South Group, quarter-finalists
Captain: Eoin Morgan/Steven Finn
Coach: Stuart Law
In a nutshell: Reached knockouts for only the second time since their 2008 title last year, but three of the top five run-scorers last year - Dawid Malan, AB de Villiers and Paul Stirling - will play no part and new captain Morgan looks unlikely to feature between England duty and the start of the IPL. Core bowlers remain but homegrown batsmen need to step up.
Star: Nathan Sowter, the legspinner who is now England-qualified, had a strong tournament last year with 16 wickets, and will be the primary spin option this season in Mujeeb Ur Rahman's absence. The main question is whether he can work out a method against left-handers, having leaked 11.10 runs per over against them over the last two seasons.
One to watch: Nick Gubbins only played three Blast games last season and has a mediocre T20 record, but has shown his white-ball potential in List A cricket and was joint player of the tournament in Australia's National Premier T20 Championships over the winter. He should get a run of games in the top three.
Verdict: Absence of batting stars will be their undoing
Last year: 8th in South Group
Captain: Jade Dernbach/Gareth Batty
Coach: Vikram Solanki
In a nutshell: Second-bottom last year but only three points off third, and there are reasons to be optimistic despite absence of several England players. Rory Burns and Ben Foakes are useful middle-order rotators, while Sam Curran should be available for at least the first handful of games and Reece Topley - a reserve for the Pakistan T20Is - could come into the picture for the second half. The loan signing of Laurie Evans is a major boost.
Star: Will Jacks was expected to have a breakout Blast in 2019 - not least after his 25-ball hundred in a pre-season T10 game against Lancashire - but didn't quite deliver, his 152 strike rate tempered by an average of 20.92. He is highly rated by England, and was named in their 55-man training group at the start of the summer after impressing on the Lions tour to Australia.
One to watch: After his unceremonious axing by England, Liam Plunkett has a point to prove. He played only twice in the Blast last year due to injury and struggled in the Bangladesh Premier League, but impressed in the Abu Dhabi T10 and will hope that a strong tournament can be the springboard to further stints on the global short-form circuit.
Verdict: In an open group, quarter finals look like a real possibility
Last year: 1st in South Group, quarter-finalists
Captain: Luke Wright
Coach: Jason Gillespie
In a nutshell: Topped the nine-team South Group last year thanks to an all-star bowling attack, and the strongest team on paper by some margin in this season's six-team version despite Jofra Archer and Chris Jordan's likely absences. International quality throughout their batting line-up, and Gillespie will be desperate to sign off with some silverware.
Star: Tymal Mills will lead the attack and carry much of the wicket-taking burden, with death-bowling duties likely to fall on his shoulders. With experienced spinners Danny Briggs and Will Beer set to operate in tandem in the middle, he will be required as a top-and-tail option. Fixtures come thick and fast, so it may be sensible to rest him a handful of group games.
One to watch: Sussex's likely top six is filled with stars: Wright and Phil Salt will open, with David Wiese and Bopara playing as finishers. But they have a gem at No. 4 in Delray Rawlins, the Bermudan left-hander, who has struck at 155 against spin in his Blast career and has licence to free his arms rather than just ticking over. There is extra pressure to step up after Evans' loan move to Surrey.
Verdict: Anything short of a Finals Day appearance should be considered a failure
Matt Roller is an assistant editor at ESPNcricinfo. He tweets at @mroller98