Here's a good tier list (mine)
Top Tier: 1tJavier, Von Bolt, Kindle, Sturm, Sasha, Sami, Nell
1tJavier gets 110/110 and added indirect defense, no negatives makes him the best nonbroken.
Von Bolts 110/110 make him automatic top tier.
Kindle has the property bonus and 3 star blight, can even take on Von Bolt succesfully (as shown in testgames.)
Sturm has 80/120 for a good d2d bonus, free movement that can make him broken, and awesome meteor powers, he too can take on Von Bolt.
Sasha is always a safe choice, good against long bar co's, but less good against Nell, Sami, Kindle and 1tJavier.
Sami has the footsoldier bonus, movement on (s)cop and the capture bonus to make her great, especially during scop she's gamebreaking.
Nell has a great d2d and even greater yet very cheap powers.
High Tier: Andy, Lash, Eagle, Grimm, Drake, Rachel
Eagle and his scop are obviously high tier, Eagle is always dangerous, especially with air and indirects.
Lash has a good d2d, and a good scop, no negatives.
Andy is somewhat bland, but a decent cop and superb scop make him high tier, and he counters a bunch of co's.
Grimm has a good net d2d, and great attack powers.
Drake has a great d2d, (extra mp and def for ships, rain immunity) and his powers do a lot of stuff, like rain, mass damage, fuel halving. 160 defense battleships and 8mp black boats make him the best on large seamaps with random weather. On maps with no rain and no navy, but with air, he's just a good medium tier.
Rachel has missiles dealing a lot of damage to the fronts (hopefully) and quicker repairs, making her top tier on small low deployment maps, and medium to high tier on very big high deployment maps.
Medium Tier: Adder, Koal, Jake, Max, Olaf, Hawke, 0tJavier
Adder and Koal have cheap cops, for movement for all units, meaning great footsoldiers, which makes them superb on some maps and against some co's.
Jake has a nice little d2d, and great artillery, making him very useful on some maps.
Max is very map dependant, low tier on some, top tier on others.
Olaf has snow immunity, but rain counts as snow, his cop is very useful, his scop is good but expensive.
Hawke has a good d2d, but a very long powerbar. He does counter some mass damage co's, but has a lot of trouble against some other co's.
Javier without towers just has the indirect defense, which is a good d2d, and a cheap cop for an early 110/110 and added indirect defense. If the map has little or no need for indirects (but most maps have) then he's low tier.
Low Tier: Sonja, Jess, Jugger, Flak
Sonja gets bad luck which kills her. I have played enough games with and versus sonja to know that this is true. She does less damage and receives more counterdamage because of that. Her cop is useless outside FOW, her scop is useful but can't save her. In FOW games she can be medium or high tier.
Jess gets 90/100 infantry, the vehicle bonus doesn't make up for that, and she gets 90/100 ships and planes too.
Jugger and Flak get some d2d boost, but not much and it's unreliable, often it's bad luck. Their powers can be useful, but don't do much, a chance of doing extra damage, but also a chance of doing fewer damage. Flak is considered to be the worst co. He's better than blan though, because of the 110/110 during powers.
edit: added Rachel
edit2: added 0tJavier