go for inverter.. 1 ton should be fine, will take bit more time in initial cool down. later on both will perform same, got this chart from a tcl website, 1.5 can be considered but 1 ton isn't an issue either, rest, upto you, you want 1.5 or 1, pick accordingly
(3.5 kw= 1 ton)
(5.2 kw=1.5 ton)