Depends on the game. In all games, vanguards tend to have both weapon combat and biotic crowd control at least partly covered, which means that the biggest hole in Shep's game is tech.
- In ME1, the vanguard is only slightly less tanky than the soldier, so you don't need one of the two tanks the game offers you (Wrex/Ash). Techs are Tali, Garrus, and Kaidan (in roughly that order). I'd go Tali OR Garrus and Liara.
- In ME2, the hole is still tech, but it doesn't matter quite as much because there are fewer geth (but more shielded humanoid enemies). You're better off taking squadmates based on the kinds of enemies you're likely to face. Garrus, Miranda and Zaeed are solid all-rounders (because of their powers); Grunt and Jacob are heavy tanks (but Grunt is superior); Legion and Tali are anti-geth specialists; Thane and Samara are good for fighting biotics/collectors; Kasumi is good against tech, but fragile; Mordin is like Kasumi, only against organic enemies; and Jack honestly kinda sucks at higher difficulty levels (she's outstanding against husks at lower levels, where they don't have armor). Pick a mix of squadmates based on what the mission brief tells you you're likely to face.
- In ME3, you need somebody to setup biotic explosions. Simple as that. Javik is amazing if you have him (because you can hate surf his Dark Channel to glory). If not, Liara or (if you have him) Kaidan will work well. Garrus remains a good all-rounder, as is Ash (if you have her). Jimmy Vega picks up the tanking role from Grunt. Tali is acquired late in the game, and is frankly kinda situational. I'd go with Javik OR Liara and Garrus OR James. Luper567 (talk)