I'll second what Todd mentioned about stem work. Some folks only consider stem cosmetics externally, but it is the inside that will have a lot of bearing on turbulence and condensation. This is one reason I would much prefer an estate Barling's in good condition, over a brand new pipe in the same price range.
As for wall thickness, I prefer a pipe with somewhat thin walls. These will force you to barely keep your pipe lit, to prevent overheating. In turn, you will have the best chance to experience the complexity of the blend you are smoking, while at the same time preventing jaw fatigue.
Some folks focus on the task of keeping the pipe lit, when they should instead understand there is no shame in performing as many relights as needed. In fact, some of the best flavor you will experience, comes from the beginning lights when smoking a fresh bowl.
When I can barely see a wisp of smoke, I am usually in the zone. That is one reason I don't like to multi task while smoking, because it is harder to stay in that sweet spot with the perfect burn.
It doesn't take an expensive pipe to have a great smoking experience, but in some cases, an expensive pipe can provide more personal satisfaction for some people.