Generally if you find a pipe with a nice open draw that doesn't tend towards gurgling, you're halfway there. If the drilling is centered on the bowl and has a smooth transition into the bottom of the bowl, you're mostly there.
Then there's the intangibles, somehow some pipes just seem to do very well with certain types of or specific blends of tobacco, almost like they were made for each other. For instance I have two pipes that I smoke dark fired tobacco out of, one is a Stanwell, the other is a Nording. The Nording really brings out the deep, sweet notes in tobaccos like GH Dark Flake or SG 1792 Flake, whereas the Stan seems to have been made for Peterson Irish flake and GH Rope...I have no idea why. Maybe it is that the Nording has a slightly wider bowl.
Also some of my pipes just seem to "puff better" than others. I have a Johs that is well drilled and has a very deep bowl. For some reason it is just not as pleasurable to puff as my other pipes. It tends to need more puffing to keep going too. Maybe it's something psychological about filling the pipe, where I pack it differently because it is so different from the rest of my pipes (huge freehand).
Then there's my no-name meer with the plastic tenon...it is horrible. Draw is super restrictive, the bowl wasn't made deep enough so the draught hole is lower than the bowl and collects bits of tobacco which clog it, the drilling is so terrible you can barely get a pipe cleaner through it. It is borderline worthless. But it looks pretty nice.