premio and rola X share parts with the local rolla, most mechanical parts are the same with the belta and vitz but they are harder ot come by than the older shape vitz and belta stuff since they shared parts with local rollas too.
if you need a larger car go for a premio, if you don't then go for the vitz, if you need somehting in between the rolla X and belta are more or les sthe same size but i'd say the rolla is larger but the belta is cooler to look at.
my personal choice (for my requirements) woudl be the belta as it's a great balance of price and size etc.
but it's all down to your requirements, certain friends of mine would rather have the premio or rollax as they like larger cars, other like the vitz because of fuel economy and small size.