King Of Colosseum II is probably the greatest game ever when it comes to in-ring action. When it comes to just a fun game, most people rank Fire Pro Returns over KOC. Depends what you are looking for. Do you want a game that is a near-perfect, visually appealing simulation of the top 4 or so Japanese promotions in KOC, or do you want an overall amazing game, with an endless amount of edit spots and immense fun, without the look and realism of KOC in Fire Pro.
Personally, I have a bias toward FPR but that's because I've never played KOCII.
KOC II is really interesting. If you want a game that perfectly simulates a wrestling match, that is it. Customization and stuff is limited (making a CAW takes weeks for a casual player due to the massive moveset, and appearances are quasi-strict), but the gameplay is MILES ahead of any wrestling game, EVER.