Best size wud obviously be what comes from the company but increasing from 15 to 16 inches i personally think wud not hurt the mileage if you go for the right tyre size aswell.
Yes there are good rim brands out there besides the chinese crap.. these include Vossen and also Lenso..
People usually recommend Yokohama Advan DB as a very noiselss and good quality tyre so i wud recommend you the same as long as you buy them from an authorized or trusted dealer.. otherwise if you go for michellins or pirellis or continentals, they too will be good tyres.. and they will be much better than the stock Euros u get..
If ur car wobbles with good quality rims and tyres, get it balanced.. the wobbling shud go away..