When my friend & I went to visit Phoenix in January 2011 we did a day tour of the Grand Canyon with Southwest Tours. I wasn't sure what to expect since there weren't many reviews for them on the internet but they looked good enough through the few things I read and now I'm really glad I went with them!
Lee was our driver/tour guide & he was chock full of knowledge on just about everything! He talked to us during the entire drive from the moment we got into the van, which in itself was very roomy & comfortable. He shared facts about each town we passed, little tidbits you probably won't find in tour guidebooks, and told us all about the different animals, plants & cactus we saw while on the road.
The group we were with was a small group of 5 people so it had a really nice, cozy feeling. Lee was very accomodating whenever we needed to make an emergency bathroom stop, which happened somewhat frequently with all the complimentary water they gave us! Haha. We made many stops along the southern rim of Grand Canyon & we were taken down on a few trails that were away from where most of the visitors usually congregate & with spectacular views so we got a chance to enjoy the beauty of nature in a peaceful environment.
I highly recommend Southwest Tours & would definitely consider using them again the next time we go out there for a visit.