having owned most and driven all of them, i can honestly say that i enjoyed my 2.4 10v the most.
it was fitted with my full system, hard pipes, c & g clutch, and a re-map from Nige at Angeltune (JTD map Lord!), but then so was my 16v in similar spec.
the 2.4 10v was an absoloute stonker, we all loved it, and it still returned remarkable mpg when required, and being the earlier 10v it has the fiat/alfa gearbox, not gm
the 16v 1.9 was lighter and livelier, and slightly better on juice around town, but lacked the out and out thump and character of the 2.4, doesn't sound anywhere near as good, but does rev on usefuklly higher than the 2.4's.
so i think it depends how you want to drive it, all the engines are great, but the five cylinder 10/20v's would be my choice everyday of the week now.
plus the 1.9's were far more sensitive to my tuning parts, regulalrly throwing a sensor fit, silly things!
that'd my two penneth, character and torque over another couple of mpg, but try them all, see what you like the feel of...
cheers, happy shopping, and good luck