Vintage Synth Repair

Hi guys,
I'm starting to get that kit building bug again, after years of
absence from the hobby.  I did it pretty heavily back in the 70s-80s,
but fell away for a while.  Question: I need a new soldering iron.  I
see wattages in the range of 15 through 40.  What should I be looking
at for assembly of electronic kits from places like PAiA, etc.?

Thanks,

Rob Williams
Portland, Oregon