I don't do it often since the big B airports are generally not anywhere near where I need to go (because people don't like airplane noise, and airports are usually sited accordingly), but IMO the only ones that should be avoided under most circumstances would be the ones like ORD, ATL, LGA, LAX, etc that are really at the highest end of the traffic spectrum and have no shorter runways and not much in the way of GA services. The Bs that I have flown into have had somewhat lower traffic levels, and can easily handle GA. For example, I've gone to BWI several times, and always been on runway 15L which is only 5000 feet so tends to be only used by GA (including small-midsize jets) and turboprops if it gets busy. No more difficult than flying into an average class C, IMO. In fact, KMDW is a C and has nearly twice as much daily traffic (688 ops) as one of the other Bs I've flown into, KMSY (364 ops). BWI has only a smidge more traffic than Midway (717 ops). The ones I mentioned above are far busier (2418/day for ATL, 2553/day for ORD, etc) Hobby has 563 ops per day, and plenty of runways to handle them. It is not Houston's "big" airport (IAH) and I wouldn't call it a "busy class B". IMO, it's perfectly reasonable to fly GA into these sub-1000-ops-per-day spots. In the 1000-1500 per day range, it depends on the time of day, runway configuration, etc but still can be done reasonably easily with planning.