Please keep us posted on this. I'm researching windows for our house as well. Lots of scammers out there, I really want to make sure I get this right.
Well, a crew of a dozen folks swept through the house, and replaced 17 windows and a sliding door in 5 1/2 hours. The results actually look really good.
The installation option we selected kept the original aluminum frames in place, and inset the new windows and frames within the remains of the old window frame. This has the drawback of giving us windows inset within a frame that's about 2 inches wide all around the window, so the actual glass is smaller. It has the advantage of not disturbing the waterproofing integrity of the existing frame, flashing, and moisture barrier under the stucco finish of the house.
The other options available involved 'pulling' the frame, effectively ripping it loose from the flashing, and leaving no real seal where water moving within the stucco reaches the ripped end of the moisture barrier, sawing most of the exposed part of the aluminum frame out and cutting the sills to insert a slightly larger window, again with some reduction in waterproofing that is partially compensated for with insane amounts of caulking, or using 'new construction' windows, sawing and hammering out the stucco to expose the window nail fin, and tearing back the moisture barrier so the new window nail fin can be set on the wood and flashed (more or less) properly. (This costs much more than the inset replacement we went with.)
The sliding door replacement used a new construction door, so there was much sawing and hammering out of the stucco. The new door was nailed in, reflashed, and re-stuccoed with a texture coat that pretty much matched the house. Casing (mouldings) were put on the inside to cover the banged up wallboard where the old door was pulled.
We got three estimates. The company we chose was a local one with a pretty good reputation, and happened to be the low bidder. The high bidder, BTW, was 35% higher, and had... oddly consistent... reviews on Yelp, which the salesman was quite proud of.
We checked the contractor license and insurance on the California license board's web site. There's one interesting bit of information we gleaned there. Some of the window replacement businesses didn't have (or need) insurance coverage, because they have NO EMPLOYEES. We ruled these right out. Either they were subcontracting to a real contractor, or the owner was going to show up on work day with a crew he found in the Home Depot parking lot. Either way, no thanks.