As has been said, the J Mascis signature is the standout because it has an unusually good neck. They are discontinued now though and I don't know what the prices are like. In the last few years of production they changed the fingerboard from rosewood to Indian laurel (in line with all Squiers).
With the discounts on Fender ones, almost seems worth getting one of them. Noticeably better? Not experienced with electric really despite a few previous dabbles.
Anyone know If there is a Squire Jazzmaster model that's a cut above the rest, but not Fender prices? Just for twiddling on rather than performing.