I don't think I've ever actually deleted a character as such, although I've rerolled a few - irritatingly, I made most of my early mistakes before they started handing out freespecs like candy - and changed powersets on a reroll once or twice. Right now I run:
Thunderforce: MA/regen scrapper 35th. My first character, so rerolled her once around 20th - she was completely messed up. For example, I hadn't known you could slot more than one of a given enhancement in a power. She was on my first Positron deathmarch - I'm a taskforce obsessive. To be fair, I've not been playing her for a couple of months while trying to get her into a Numina run so as to get Task Force Commander at the lowest possible level.
Pressure: "pure" empath/energy defender 31st, so dates from my very early days when pure empathy and the Hollows seemed like a good idea. I've stuck with the concept, but shuffled some slots and taken Assault to ease the soloing pain. I'll play her out, but it's not a character I would create today.
Banestorm: inv/SS tanker 31st. Never rerolled, but changed with the defence nerf from a pure meatshield to a more balanced build. The pre-nerf version of her was ridiculously overpowered - I see why they did it. She's entertaining now, but tanker isn't really my favourite part of the game.
Zakuko: energy/energy blaster 29th. My single favourite character. Godlike teamed with kineticists. When I started her I had not yet been exposed to the blapper idea, so she first had the conventional idea - 2 basic zaps, the cone, the sniper power, take the secondary powers just to fill in gaps and use when enemies got close. Then I noticed every time I used the cone every enemy in it made a beeline for me and beat on me - apart from the first one to reach me who generally got the Bone Smasher in the chops and went down. Rerolled her along blapper lines, but still had not completely had the epiphany - she only got Energy Punch in the mid-20s and wondered then why she'd carried around a silly sniper power instead of it.
Sixth Sense: fire/FF controller 29th. Force field is not a bad choice for a controller. The downside is limited self-defence; the upside is if you want to concentrate on controlling, your secondary takes few slots and each teammate only needs your attention once every 4 minutes - hence the endurance requirement is also low. Rerolled - her initial build was utterly botched - but now highly effective on teams and a tolerable soloist with Hot Feet.
Necessity: BS/inv scrapper 26th. Although I'll always have a soft spot for Thunderforce, Nec's my favourite scrapper. She started pre-defence-nerfs trying to get by with just the passive powers, so had to be completely reworked after that. BS/inv really struggles for power selections early on.
Scamp: fire/energy tanker 24th. Created long after fire had been defanged, so you won't catch me whining about Burn. A lot of fun, albeit rather fragile next to Banestorm.
Gemako: kinetics/en defender 23rd. Kinetics is a barrel of laughs; skipping travel powers means extra power slots early on and the set's core powers are very effective - and, as defenders go, Siphon Power means your soloing isn't quite an anaemic as most.
Red Flag: energy/fire brute 15th. I got CoV almost when it came out - I just don't play villains much, which is why I only have three.
Defiant gets all the joke characters:
Toronto: FF/psi defender 21st is, of course, from CANADA. Created to enjoy the opposite of empathy's hyperfocus on the health bars - bubble everyone and then blast away, it's not like you can bubble them again.
Braaains: dark/regen scrapper 18th. He's there to play a rascally zombie; his chara design predates CoV and the zombie parts.
Pieces of Eight: en/SR stalker 10th. Rerolled from en/regen. Why Energy Melee? The Bone Smasher. I've had him a while - don't know why he hasn't progressed more.
Zombina: necro/dark mastermind 12th. Started as necro/ff, but rerolled into /dark. Why? Because the work to be done with /dark does not increase as the number of teammates and minions does; /dark's really the most viable MM secondary to me for that reason alone.
Glasshouse: illusion/rad controller 10th. I wanted to know what the flavour of the month tasted like, and to have an ill/rad who isn't some Magic Origin girlie.
Kid Sister: energy/energy blaster 10th. Zakuko's so much fun, this is just her again with the exact build progression she should have had from the start.