Which crankset is a better value
 

Which crankset is a better value for the money a Shimano 105 triple or a Bontrager Race Triple GXP Crankset w/ External BB ?

Shimano hands down

They're both probably equally good - so not knowing the retail or what deal you've been offered, I'd go for the cheaper one.

Problem with Bontrager is that it has the 'house brand' stigma, even though the components are perfectly good. This is very different from 'Colnago', 'Pinarello' or 'Bianchi' branded components which you know are actually Campy, Deda, Cinelli or ITM manufacture.

Just remember that Bontrager stuff is rebadged TruVativ. To me, it would come down to a personal, esthetic preference

I think Shimano has the best rings.

IMO Truvativ rings are questionable, not exactly the stiffest crank either.