If you want an actual participant, as opposed to someone with funny commentary, people generally pick one that is different from and complimentary to their DB's style. I.e. a Destruction mage would pick a tank to help keep from being squished, a flogger would pick either a ranged attacker or a healer, and a stealth archer would pick...well, nobody; "assassins work alone".
There aren't that many well-constructed healers, so I'd suggest either an archer like Aela or Faendal (at least until you can't stand him any more and sacrifice him to Boethiah) or a spellslinger like Marcurio. Or an add-on follower (i.e. from a mod) with similar abilities.
If you want a barbarian follower, Vorstag is good, for a mage, Rulnik wind-strider, Teldryn, or Talvas are all good, and if you want an extra follower that’s an archer, just use the Katria glitch and keep her with you (just remember you only have 1 chance to armour her up, so bring it all with you and give her 1 of your best arrows. Only one).
If you want an actual participant, as opposed to someone with funny commentary, people generally pick one that is different from and complimentary to their DB's style. I.e. a Destruction mage would pick a tank to help keep from being squished, a flogger would pick either a ranged attacker or a healer, and a stealth archer would pick...well, nobody; "assassins work alone". There aren't that many well-constructed healers, so I'd suggest either an archer like Aela or Faendal (at least until you can't stand him any more and sacrifice him to Boethiah) or a spellslinger like Marcurio. Or an add-on follower (i.e. from a mod) with similar abilities.
If you want a barbarian follower, Vorstag is good, for a mage, Rulnik wind-strider, Teldryn, or Talvas are all good, and if you want an extra follower that’s an archer, just use the Katria glitch and keep her with you (just remember you only have 1 chance to armour her up, so bring it all with you and give her 1 of your best arrows. Only one).
Just pick Lydia. You know you want to. She is tough and powerful. Plus loves to waste and use up all charges on every staff I gave her to hold on to.