Boss fights for me are easy once you have their patterns memorized. Here's a few tricks that have worked for me, and maybe they might work for everyone else.
Firstly, I have found that starting a punching combo, then finishing it off with a grappling combo usually does the most damage for every character (depending on their power stat of course). I.E.: B, B, B, forward walk/dash into stunned opponent to hold them and keep holding forward, B, B, B (some characters like Shiva have an extra B... characters like Axle end the combo on that last B, so for those characters, only 2 B's) then either back B to throw, or flip over (c button) and then back B for the more powerful move (I.E. Blaze's German Suplex). Max is the only one where you can let go of forward and just hit b after the first two grappling BB combos since he does that bearhug that hits 5 times. It's highly recommended that you don't attempt this on Abadede though, as he can easily (and quickly) counter out of it.
SOR1 Bosses (for the SOR1 route):
Boss 1 (Antonio): Easiest of boss fights. Approach him from the side (walking up or down to him) since walking straight to him will result in him kicking you in the face. Attack him once you're close enough.
Boss 2 (Zamza): This one you have to play mind games with cause everytime you walk towards him, he walks away, and everytime YOU walk away, HE follows you. There will be moments where he will try to get to the other side of you (I.E. he moved up/down, then foward to get behind you). Thats when you attack him. Otherwise he will claw you to death.
Boss 3 (Abadede): This also works for SOR2. Since this guy is practically invincible at times, the only way you can attack him is to use the side trick like in the first boss, only NOT SO CLOSE! It's recommended using a character that has a far reach when it comes to attacking (Shiva/Zan/Elle, ect...) keep punching him a few times till he ducks down to attack. As soon as he ducks, move the opposite direction so you wont get hit. Keep doing this for a while till you finally beat him. if done right, you won't get damaged at all.
Boss 4 (Big Ben): Really easy if its one, semi-easy if it's two. Big Ben has a pattern of moving diagonally up or down when he shoots his fire depending on where you are located. once you avoid him and he passes you, immediately attack him from the back. But remember, this guy you CAN'T pick up or else you will get hurt as well (like the SOR3 Big Bens... the SOR2 ones you can throw around like normally). If it's two Big Bens, try to see if you can get them to go in the same direction so you can attack them simultaneously... otherwise alternate between the two till you only have one you can kill easily.
Boss 5 (Mona & Lisa): The easier version than the SOR3 version (mainly since they don't move backwards when you hit them). Once you attack one (or both if you're lucky), make sure you're right on the attack slightly before they get fully back up, that way they wont be jumpin around all the time kicking you. Just keep in mind to not throw them cause they always safe land (unless you're using a SLAM throw attack like Shiva's back throw).
Boss 6 (Robo Y): Annoying as hell, but can actually be defeated. He's always movin in a circula pattern. Attack him when he gets slightly close (safer if you use a character with a far reach attack like for Abadede). After you finish the attack, move up or down to avoid him, he will go back to his circle pattern. At times he will shoot missiles, which you can easily avoid by moving up and down. Keep in mind that combos rarely work for this guy, so you might either have to use jump attacks the whole time, your special move, OR a jump down attack (C down) to follow up with a combo.
I'll type up more for the SOR2 & 3 bosses tonight when I'm home and have more time.