I'll support Lancer, since he's a good ally and a bro. He's definitely experienced in many ways and could act like a big brother to Shirou.
As for the ladies, I'd go for Rin, Kohaku, Saber, Bazett, Caren and Hisui.
Rin, Saber and Bazett could work well with Lancer as well, and potential for romance with him could be a possibility. Maybe.