Imo just dont get something under 30W, unless ure doin SMD-only work. Also anything above 50W without thermal regulation is too much.
U might want to try to build ur own soldering station, its fun little project. These soldering irons just have buildin thermocouple, all u need is some kind of voltage reference, low Vos opamp ( i used OP-07) and few other common parts (mine uses opamp as comparator + triac/optotriac (with zero detect) for driving iron))