We've done the last three Ride the Rockies (RTR), and because of the route, we're very seriously considering Bicycle Tour (BTC) this year.
All three times, we debated which tour to do, and have done as much research as possible. As best we can tell, differences are:
1. Daily rides are generally a bit tougher on BTC, but BTC has a rest day. RTR is a bit easier (less aggressive climbs and slightly shorter mileages) but you ride every day. Of course, the rides are both in Colorado, and tough days are inevitable on both rides. I would say that BTC attracts a slightly more hard-core group.
2. RTR has better vendors supplying food along the route. BTC supplies better food at the rest stops. BTC has fruit options, PBJ's, cookies/crackers. RTR has bananas or oranges. BTC has one lunch option. RTR has a group of vendors that set up at all the rest stops, so you can get burritos or burger or smoothies at the rest stops.
3. Both have full motorcycle police escorts, same camping situations, but different hotel options. RTR has a vendor that will do luggage transfers to all the hotels, and you book the hotels yourself. BTC has a vendor that books all the hotels for you and transfers your luggage -- if you book them yourself, you're on your own for getting your luggage back and forth from the ride headquarters in each town.
4. Both seem to be incredible - I've heard nothing bad about either, and I can't wait to pick which one to do this year too. I'm even considering doing both, back to back!
For 3 days, I get to part of a thousand other journeys.