Hmm, I've at least tried most of them. My impressions:
Vi ~ Useful class (Valkyrie), nice personality, also she's an old friend from the days of Wiz 7, won't follow you into Rapax Castle, Bayjin or Rapax Away Camp
RFS ~ Good class but unable to cast spells, will follow you into all areas except Rapax Away Camp, funny dude
Saxx ~ Useful class, cool dude
Myles ~ Annoying as hell, but gives you some side quests and tipps (but you can get those without recruiting him), will follow you into Rapax Castle
Sparkle ~ Ultra-cute, but of limited combat use, won't follow you into any special areas except the Umpani base (where you can recruit her). Main use, like Tantris, is as a starting companion if you start from Mount Gigas.
Madras ~ Funny dude (Trynnie), useful class (gadgeteer), won't follow you in the games' later areas (Rapax, Bayjin, Ascension Peak)
Tantris ~ Samurai, his main use is as a starting companion if you start in Marten's Bluff (by importing your Wiz 7 savegame). If you start in the monastery, he won't be of much use when you finally reach him. He's the only lasting T'Rang companion, though. Won't follow you into any special areas
Urq ~ A Mook and I found him pretty annoying, nearly on the same level as Myles. He gives you gold for any newly discovered (read: first entered) location. So it's the best strategy to hire him early on, but in order to do so you need a Mook in your starting party. He will only follow you to Marten's Bluff, but not to Mount Gigas or any other special locations.
Sexus ~ He's actually quite useful and powerful. He also will follow you everywhere except Arnika. But there's a huge tradeoff - he will betray you if you fight any Rapax. He will be the last RPC you meet and by then most player's will have a grudge against the Rapax, I think
There are three more temporary companions (Glumph, Drazic, Rodan) who will follow you temporarily in order to fulfill certain quests. The game is designed to provide you with the necessary free slots to recruit them (only one of the early available characters will follow you into Bayjin and no characters will follow you into the Rapax Away Camp at all).
Vi ~ Useful class (Valkyrie), nice personality, also she's an old friend from the days of Wiz 7, won't follow you into Rapax Castle, Bayjin or Rapax Away Camp
RFS ~ Good class but unable to cast spells, will follow you into all areas except Rapax Away Camp, funny dude
Saxx ~ Useful class, cool dude
Myles ~ Annoying as hell, but gives you some side quests and tipps (but you can get those without recruiting him), will follow you into Rapax Castle
Sparkle ~ Ultra-cute, but of limited combat use, won't follow you into any special areas except the Umpani base (where you can recruit her). Main use, like Tantris, is as a starting companion if you start from Mount Gigas.
Madras ~ Funny dude (Trynnie), useful class (gadgeteer), won't follow you in the games' later areas (Rapax, Bayjin, Ascension Peak)
Tantris ~ Samurai, his main use is as a starting companion if you start in Marten's Bluff (by importing your Wiz 7 savegame). If you start in the monastery, he won't be of much use when you finally reach him. He's the only lasting T'Rang companion, though. Won't follow you into any special areas
Urq ~ A Mook and I found him pretty annoying, nearly on the same level as Myles. He gives you gold for any newly discovered (read: first entered) location. So it's the best strategy to hire him early on, but in order to do so you need a Mook in your starting party. He will only follow you to Marten's Bluff, but not to Mount Gigas or any other special locations.
Sexus ~ He's actually quite useful and powerful. He also will follow you everywhere except Arnika. But there's a huge tradeoff - he will betray you if you fight any Rapax. He will be the last RPC you meet and by then most player's will have a grudge against the Rapax, I think
There are three more temporary companions (Glumph, Drazic, Rodan) who will follow you temporarily in order to fulfill certain quests. The game is designed to provide you with the necessary free slots to recruit them (only one of the early available characters will follow you into Bayjin and no characters will follow you into the Rapax Away Camp at all).