looks like they both have the exact same drive train so the difference is 100 aluminums. (100 vs 200). no idea what that means but I've heard good things about the ALR models if that's worth anything to you.

You'll probably get some negative feedback about the 9 speed Sora but heck, even the $1700 aluminum domane has Tiagra! What the hell, Trek.

I'd say go test ride the thing and buy the one you like more. if you can't tell the difference between 100 series AL and 200 series then you certainly don't need to pay for it.

Some other options in that general price range:
Cannondale CAAD12 105 (about 1600)
Cannondale synapse disc 105 (about 1500)
Specialized Allez Elite 105 (1200)
Felt FR60 10 spd tiagra (1300)

I say "general" because you can likely pick up last year's model for 20% less once the new models hit the streets. One important consideration is to find a shop you like, of course and I don't know what's available in your area.

Happy hunting!