I've always liked the sals, I would think a pair would do nicely in a 30, they can be pretty aggressive, so it may limit your options for other fish to go with them (I wouldnt dare put cories with my 6" convicts), and you might want to have a divider ready
you could maybe put in a school of 6-10 tiger barbs with them, and a small pleco
(just so you know I dont own salvini, cant promise this will work, just suggestion)
if you go with something smaller than salvini, you might be able to fit more cichlids
*edit* was reading elsewhere barbs may not be the best choice with sals