SOCOM 2 and this game our very close for me but I'm going to say yes combined assault for me. Just because that's where I created my clan that I played with throughout that game and those memories are just unforgettable. Best gaming time of my life. Socom 2 still had those amazing times though.
Gotta say SOCOM II with a SOCOM I closely tailing. Originals are usually the best, but how can I not choose II if all it did was simply add to the experience keeping the gameplay almost identical, adding a new campaign, keeping every map and then adding more, and creating another amazing soundtrack.
I did also like SOCOM 3 and CA, but I would have loved them just as much without the "SOCOM" on the box :/