Should I use 10/2 wire for a lengthy 20A circuit?
Unless the run is extremely long (we're talking 200 feet) or has a high sustained load you won't have any problem with 12/2.  Most tools/appliances I know of are designed to work properly down to 110v.  Assuming a voltage drop of 3% you are still comfortably above 110v, unless you anticipate a sustained heavy load near max capacity (20A) that will start heating up the wire more than usual.

Working with 10/2 is much more cumbersome than 12/2 in in standard receptacle boxes if you're pigtailing (parallel circuit). It's even more cumbersome when it's not necessary.