I would recommend anything by DLPB, (menu overhaul project, retranslation project, fmvs, ost), covarr's music installer, omzy's field pack, and a gameplay mod (i am interested in Rebirth). Also, DLPB and pitbrat made a unified model installer which contains every available model (i recommend PRP, squallff8's models, and every minigame model). With these mods you will essentially get a comprehensive overhaul while nothing being noticeably out of place. What do i mean by that? Well..
It's true that some models have been made in really high quality and look awesome, but they were never finished as a comprehensive mod. Felix made an awesome world map mod, battle scene enhancements, magic texture replacers, and a cid model, but as far as i know none were fully completed. Milena made an awesome sword set for cloud but it looks out of place if he is the only one with cool weapons. Team avalanche has a LONG way to go even though what they made is awesome, but it still sticks out amongst the rest of the game while unfinished. Personally, i love these high quality mods but i won't play while using them until they have become comprehensive. (All weapons in hd, or the entire world map).
But i guess it all depends ob preference. Check out my first list of recommendations for comprehensiveness, but check out my second for eye candy. Note: the menu overhaul project is both comprehensive and eye candy.