Now that I have your attention, I add my disclaimer: in my many tours, these companies stand out as providing excellent service and tremendous cycling experiences. I haven't included those that did not exceed expectations, nor have I taken all of the tours available. These are merely my opinions.
Highest on my list is Velo View Bike Tours. They specialize in five day rides, sometimes with an extra cycling adventure if you come a day early or arrive early on the meeting day. Shannon Burke has picked some spectacularly scenic spots in Colorado, New Mexico, California Wine Country, and Texas Big Bend. Also Virginia, Carolina, and Kentucky rides provide superior cycling venues. Most of the rides include strenuous climbing, but that is moderated by his willingness to tailor the experience to the individual, so if you need to sag in or hitch a ride to the top, just let him know. Shannon rides with the group, which is usually limited to a maximum of eight riders. The wine country rides are more gentle in nature. Also featured are "bike retreats." Long week-ends, three days of cycling. When not doing the tours, they offer day-trips in the Texas Hill Country. For the locals, or for someone coming to Ausin on business and wanting to get in a workout, these are great.
The most difficult, by far, bike tour I've taken was with Black Bear Adventures. Paul Wood specializes in touring the Blue Ridge Parkway, although his other signature tour is the Natchez Trace. His motto "Vacations Designed for the Avid Cyclist" is somewhat misleading. If you want to do the Blue Ridge Parkway (and you should, this is an A++ ride) you must be in really good shape. It isn't necessary to be able to challenge Chris Froome, but definitely be above average. Paul also limits his group to a manageable size. He also will do private/custom rides or offer guiding services.
Next on my list is Bike Adventures. They specialize in tours in Europe, but are based in England. I did the E2E ride and was quite pleased, although there has been a change of ownership since my adventure. They offer a wide variety of tours at a very reasonable price.
If you have read either of my books, you know that for anyone wishing to experience Le Tour de France, you should look no further than Marty Jemison. The rides, the experiences behind the scenes with the pros, the food and wine.... I can't come up with sufficient superlatives (read my book if you want more depth).
Now, if you want to go coast to coast... Who hasn't dreamed of doing this? Again, first read Bicycle Journeys with Jerry, then click on America By Bicycle. Going coast to coast is difficult enough just to cycle. Let ABB do the logistics, they take really good care of you. They pick the best, safest routes, provide van and sweep support, good hotels. Their guides are the best.
One more thing, please don't send me any comments on this post, positive or negative.