Congrats! I was also choosing b/w these 2 recently. It's a tough choice for sure.
Re: "choosing a specialty before starting research," students have time to shadow during preclin SMS to figure this out, but I've also heard of people deciding on their specialty last minute and still matching to their favorite programs. Regardless, at either school, you can start research whenever you want.
Overall, these 2 schools are REALLY different, so you're going to have to look inside yourself and ask what is truly important to you. Flexibility or structure? Local support systems or can you make new friends and handle LDR? City amenities or nature? 1 campus vs. many? Higher chance of matching on West coast or East coast? Huge or small class? Awesome weather or does that not really matter to you as much? Etc.