My personal experience and advice would be to not fly into Houston. I have done so twice before, and both times have been horrible experiences. Both times I was held in immigration for close to two hours, missing both connecting flights. My flights were under different circumstances, as I was staying longer than two weeks, and I fly to the states pretty frequently, so Im probably much more likely to be questioned I think, but still for every airport I have flown into, this is the only one that has given me any trouble in the sort. This doesnt mean you will certainly get hassle, chances are you wont have any problems at all, just my experience. I would personally take a look at Phoenix, however, if you are going without much to do, and are willing to go anywhere, im not sure Phoenix would be my first choice. Its a nice city, but there isnt a great deal to do there or see to be honest, and the same goes for Scottsdale just down the road. Some very cute places including Sedona and Flagstaff a bit of a drive away though.
IAH isn't a bad airport at all. You are right about the long lines at immigration, but these are only a problem if you arrive at the same time as the FRA, AMS and DBX flights. If you get in before these you are likely to be through within 20 minutes.
I was in Phoenix just over a month ago and I wasn't impressed at all. Just another carbon copy, very business like city, much like Houston only smaller and quieter. Sedona was pretty but very touristy.
To visit, Houston gets very boring after a few days. There isn't a great deal to do. Teh same goes for anywhere in Texas really. Austin is where it's at but any more than a week here is far too long. I'd recommend travelling around, especially if you can get your hands on a car. If not, bussing or getting the train can make for an awesome trip!
My favourite hub, until United stopped flying direct from LHR, was Denver. Flying in there was always a pleasure. Friendly staff, almost no lines and one of the very few "cool" airports I've been too. The beauty about Denver is that you can get out of the city easily and you have a good choice of things to do or places to go. The Colorado people are brilliant. Hospitable, friendly, great fun and they will make your trip memorable.
I'm at work right now so haven't had a chance to check out flights but I'll look when I get home. In the meantime you can check out these:
www.fly.com
www.kayak.co.uk
www.skyscanner.net
www.expedia.co.uk
www.orbitz.com
www.continental.com
www.united.com
www.ba.com
www.aa.com
www.delta.com
Some basic tips when booking:
-Flying on a Saturday can often bump the price up significantly.
-Tuesday and Wednesday are often the cheapest days to fly on trans-Atlantic routes.
-Don't get too hung up on which airline to fly with. Yes, some have better IFE and food but tbh it's only a fraction of your holiday and you should use the flying time to catch 40 winks. When you're sleeping, pretty much all economy seats are exactly the same. Choose the flight which is easiest on your wallet and has the better logistics.
-For those days, the sooner you book, the better. Sometimes you can get a slightly cheaper price by booking last minute when passenger loads are very low but your trip is during peak season and this isn't very likely, especially on the routes you are considering.
-If you want to stick to Houston, if I were in your shoes I'd be flying out on Continental CO35 or CO5, LHR-IAH.
P.S. if you do decide to travel around a bit which I thoroughly recommend, be it by car, bus, train or plane, I recommend visiting New Orleans. If meeting interesting people is what you want to do, this is the place for it
