blitz or lux

It depends on what you want. Lux is best as a mid laner, but can be used as a support while Blitz is almost exclusively a support. If you are in need of a tanky support you can get Alistar (and a skin) free from Riot by submitting a ticket and requesting Unchained Alistar, which will free you up to get Lux to serve another role.

I personally prefer Blitzcrank though, because I am a Support main and he's my secondary pick; he's very good against lower elo players that can't dodge his hook and easy to use.