Guessing you dont want to hear this but go to bike shops and test ride these bikes. A few you will be able rule out right off the bat and be able to narrow it down to an easier choice. Ride around their lot or whearever as long as you need to. And try a couple of bikes you had not originaly considered, you might be suprised at what you like to peddle versus the analysis paralysis.
Try not to let $100 make the decision, you wont care about the money after 3 weeks or 8 months or two years of riding a bike you enjoy but you will regret not spending it if you dont like the bike.
You say 12-15 miles 6 days is your plan that is good to know. I ended up riding double my plan so keep in mind that you may fall hard cycling, or you may just ride your plan.
Lastly consider the quality AND comfort, hopefully these two qualities will go together in one bicycle as they should.
Good Luck