I would like to second the "no extra knots" comment. I think if a rope halter is considered to have more "bite" then it should be treated as a training tool similar to a leverage bit. A web halter, while easier for a horse to lean on, is more forgiving of beginner's mistakes, and I would compare it more to a snaffle bit, in that it has more potential to be mild.
I get so annoyed when people say "he can't lean back on those knots on the poll or nose, etc", well, no, it HURTS! I feel any horse that's truely halter broke, doesn't need the bite of a rope halter to feel the cues, and will respect a web or leather halter as well as narrow rope one. For beginners, the buckle of a classic halter is easier to figure out, and beginners should hopefully (in an ideal world that usually doesn't happen, I know) have a horse that's halter broke and it doesn't matter what kind they want. My bubby, still has trouble with that knot on the halters, and his are forever slipping off, etc, so the web is just easier, and actually ends up being safer in that instance.
Also, I love my web halters. I use a kind that wraps under the jowls so they can't rub off, and I like the "feel" I get with them. I compare it with a cheap,nylon rein (rope halter) and a heavy leather rein (web halter). The leather just provides more "feel" to the bit, or a good lead rope, vs a not so good one. The rope halters feel more like they let the lead "flop" and the web ends with a solid bump when I need to tug on it. When you go to put on a web halter, the noseband tends to stay open easier, a rope one is flimsy, so it tends to close up, (but I order quality ones with nose wraps, that help with that some), so it's just easier overall to apply a classic halter, IMO.
I do use rope halters, they are easier sometimes to adjust to many different horses, and if you have a puller, they don't break. But they are much more apt to hang on something, and I just like them for training for respect,but ultimately, I prefer the web, personally.