@topher, Neo Geo Cup '98 is an updated version of Super Sidekicks 3 which had been released in the World Cup year 1998. Super Sidekicks 4, aka Ultimate 11, has a different engine than the prequels and generally is considered the worst Sidekicks title, it just looks a bit prettier than the others, that's about it.
My personal picks for the best Neo football games are:
- Neo Geo Cup '98 (homecart-/MVS-only, has all the teams and stadiums from SS2 and 3 + a few (minor) updates and the complete world lineup of teams. Excellent engine, quick gameplay, easy to get into, decent-to-good graphics, very nice game)
- Super Sidekicks 3 (see NGC'98)
- Super Sidekicks 1 (has different engine than the prequels, some people prefer it over the other Sidekicks games, give it a try)
I also played the other Neo football (cough*soccer*cough...) games and the only one I found interesting (not too hot though) was Futsal (CD-/MVS-only, aka Pleasure Goal 5-on-5 Street Soccer), it's a no-rules backyard footie game by Saurus with pre-rendered graphics and a weird but funny engine with super-moves/tricks and all that stuff. On the downside, gameplay can get a bit hectic due to comparably large character sprites but small playfield.
Depending on the Neo systems (MVS, homecart, CD) you own, it's probably best to go with Super Sidekicks 3, it's available for all system variants, has same gameplay as my fave NGC'98 but normally is cheaper.