MG Chemicals, Chemtronics, Edsyn are all good.
As for size: I have them all and use them all. The wick size needs to match the joint being cleared. Too wide and you contact adjacent things you don’t want to wick off. Too thin and you saturate the wick way too soon, so you have to use up a lot more wick, and have to heat the joint much longer than necessary. (Don’t forget that the price of solder wick is largely independent of width (with many, you pay about the same for the same length regardless of width), so wide wick sucks up a lot more solder per dollar.) Onoy the very widest wick (which many companies don’t make) is disproportionately expensive.