My top 15(In order):
1. Shang Tsung - He can morph into anyone, so you can chain combos with several characters in one go! The possibilities are huge, but without morphing, he is one of the lower tier characters. You can still do some neat stuff with the Ground Eruption and the fireballs though.
2. Kabal - He is a beast in UMK3, but he is even better in MK3! Higher damage and more combo variations work. Example:
http://www.youtube.com/watch?v=9J0x_5HJaWk - Those saws can't chain in UMK3.
3. Smoke - Used to be my favourite. He has combos ranging from fairly easy like Teleport. Spear, to improved versions of those like Teleport. aaHP. Spear to insane corner combos and punishers. Some of his punishers do ridicilous damage and his corner combos are really good, too. His spear is great.
4. Sindel - She has a nice, basic midscreen combo similar to Kabal's "version" which can be improved with 2 aaHP attacks. You can also do some crazier stuff with a jump kick after the pop up. After an aaHP you can do several FFF+HP scream moves for really high damage. Her corner combos aren't much better unless you use the flight cancel, which is really hard(aaHP. BBF+HK. Block. Repeat...). -
http://www.youtube.com/watch?v=BDk92mmjKBo
5. Nightwolf - It's great that you can use his axe in a dial combo, something they added in MK4. On some characters you can do several of those attacks and end neatly with a shoulder charge. You can even do 100% combos in certain situations like that. Best way I can think of is morphing into him after Shang Tsung's Ground Erruption.
6. Kano - He has some pretty powerful combos. They can be pretty darn insane when using his cannon ball to add more damage. His mandhandle(DF+X) move can be used to chain the cannon ball.
7. Sub Zero - His ice clone is brilliant! Can't use it in UMK3 like in MK3. Creating one in the air and then knocking the opponent into it opens some cool juggling possibilities, which aren't that high midscreen, but they are still cool. His true highlight however, is his corner potential. You can definitely do several 100% combos there. You can even start with a throw! -
http://www.youtube.com/watch?v=dYRprMC0zXU - Compare it with this UMK3 variation:
http://www.youtube.com/watch?v=6myyafBC0ww
8. Cyrax - This guy has too many very high damage combos. His bombs can be used to build up some insane combos, but some set ups are almost impossible in high level matches. Still, it's fun to do them when practicing. You can also start some chains with his throws and his air throw is nice after some anti air juggling. -
http://www.youtube.com/watch?v=yTO1WBgtYo0
9. Sektor - You might not agree here, but he shares some combos with Smoke. But instead of using a spear you usually end the combo with a rocket. His launch combo is nice for jump attack/rush starters, but you can't chain much after that unless you're near the corner. He still has some really high corner combos that only use his teleport punch, so he shares those with Smoke. Also, his homing missile can be used for some cool chains as well.
10. Stryker - He has several infinite varities in the corner and a midscreen one. I don't use them, but they are the easiest infinites I know in this game, however, I just prefer ending with a bomb shot.
11. Jax - I barely use him, but after his insanely long combo you can chain a lot of cool stuff in the corner. You can also chain a sweep after his shorter combo midscreen or a ground pound after his really long combo which takes a lot of damage. Other than that you mostly rely on punishers, but they are insane in the corner.
12. Kung Lao - I hate doing his spin move, but it's useful if you wanna start his infinite, which I don't use anyway. I prefer doing the dive trick once or twice and then ending with the hat throw. That move can be used to chain even more attacks in the corner and his teleport kick can be as well.
13. Sonya - Don't really like her, but there's a bit potential after her pop-up. Her leg grab takes a lot of damage.
14. Sheeva - To be honest, I like her more than some of the characters above, but she doesn't have that many combo possibilities. Her long dial combo does a lot of damage and you can chain the ground slam after that. Her pop up is useful and you can chain a simple jugle with a fireball or a roundhouse followed by a ground slam at the end. It's nice that you can also do stuff after her throw. Fighting her sucks cause of her collision mask, but that just gives her a little advantage.
15. Liu Kang - He does not have a pop-up move in MK3 which makes him even more useless for me. He doesn't really do high damage and to be honest, I haven't really tried him much, so here he is, at spot 15.
