What costs A LOT and takes A LOT of skill is weaving new work into old.
There's little of that.
The GC is blowing smoke.
There's NO WAY 'his guy' can do a quality job for less than your lower bidder.
The low bidder is too low for this work. His prep has got to be leaving out a step of cleaning and he's got to be doing less finish coats.
The high guy is off the charts. Is clearly quite busy and doesn't NEED your job.
Concentrate on your middle guys. Ask to see a job similar to yours. Talk with clients. (I always offer this. Any real professional won't be offended. It confirms to me how serious you are and you want high quality work.)
Ask them to clarify their specification. What exactly they're going to do and which products they're going to use.
Are they both including removing and resetting base trim or base shoe?
Are they including new trim?
How close will their match be?
Are there differences in warranties against cracking, heaving and discoloration?
Have I answered your questions?