The one thing I'd say about talonflame, is that what he does is rather unique. He not only one of the fastest priority users in the game, but he has one of the most damaging priority moves in the game, throw in the fact that the only pokes that resist flying are rock, electric and steel, the first two are surprisingly uncommon in OU, and the latter is normally hit hard by Flare Blitz. He is, for the most part, the ultimate revenge killer, and the ultimate late game sweeper, all in one, while being great in a volt-turn team, actually, he can fit into almost any team and fill in a role just as well, if not better, than someone else on that team, he is a major reason rotom-W is SO popular. I don't know if that classifies as an S tier or not, I'll let everyone else debate that. Talonflame is versatile not in the sets he uses, in the moves he uses, but the roles he can achieve at any one time.
As for Rotom-H, as much as I love the guy, I'd have him as a B. He is a good pokemon, he absorbs both burns and Paraylsis without a care in the world, only has 2 weaknesses, and overheat is a great move... but I feel 9/10 in building a team, Rotom-W would fill his role better than he would, Rotom-W isn't weak to stealth rocks, generally making him a more efficient defensive pivot, I'd also say Rotom-W is more effective as far as attacking moves go, a lot of ground pokes won't be willing to switch into Rotom-W volt switch, fearing a hydro pump, while with rotom-H, an overheat is generally, less of a risk. Rotom-H also loses out against Rotom-W and Heatran, two very good and common defensive pokemon. Rotom-H scarf does revenge M-Lucario rather well however, something which Rotom-W can't boast. I'd say it's a B right now, but it does have promise of possibly moving up in the future.