Executive Valet Parking is the best, and I've tried most of them.
I'm a (mostly) lifelong CT resident, and have flown out of BDL a few dozen times. Executive Valet Parking is on Rte. 75 (Ella Grassso Pike which runs right along the eastern boundary of the airport), just north of the Airport and the ANG station in Suffield (just over the line from Windsor Locks.)
They have very cheap rates (cheaper even than the park it yourself $6 a day "economy" lot run by the airport). They provide true valet service (e.g., when I returned in December and there had been a snowfall while I was gone, my car was cleared of snow, engine running and heat on when I returned). They also have a "frequent parker" discount card which will earn you services (free carwash, etc.) or free parking after you park there so many times.
Their van driver was quite professional and was very helpful with the bags.
The only other suggestion I would offer -- if you have an early morning flight, I would recommend staying over at the Bradley International Inn, a small motel near the airport -- for the price of the room for one night they'll let you park for nothing while you're gone, offer free continental breakfast delivered to your room and a free shuttle to the airport and back upon yhour return.
So there's my ideas; hope they help!
Regards,
Joe Hurley