Given the similarity of the parts concerned, I would ask myself whether it's worth the hassle of changing things around.
Both frames are aluminium and I think of a similar standard?
105 10 speed is a decent groupset - I run it and Ultegra 10 and don't notice alot of difference.
As for the wheels - I would probably weigh them and use the lighter set as 'best'.
My thinking would revolve around which bike to use for winter based on whether either has clearance for guards/eyelets. I don't enjoy riding in winter without them. So I'd be thinking along the following lines:
Assuming you can fit guards to only one, I'd do that and use it for winter. And the other for summer. The only change in components I'd make would be to put the lighter wheels on the summer bike (with a change of cassette if required of course).
If you can fit guards to both, then I'd use the Giant for winter and the Trek for summer (105 10 speed being all round slightly better in my view than the mix of components on the Giant). Again the lighter wheels on the summer bike.
If you can fit guards to neither, I'd get rid of the Giant and the heavier wheels and get a bike for winter than you can fit guards to.
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