Depends. If you're talking about a fast victory, you're most likely taking about a destruction deck. A well-made destruction deck, when faced with another destruction deck, can best it's opposite pretty quickly if the right cards come up. It's got a lot less chance of doing this against a more defensive setup, like builder or resource; because there's all kinds of cards that can put defenses together faster then the destruction deck can tear them down, Mountain Sentry being a prime example.
That's why when I'm playing seriously (as opposed to experimenting with new layouts) I usually play Alliance; it's a solid, well-rounded foundation that doesn't leave much to chance. I don't have a 20-turn window in which I either get the right few cards or I lose; I raise facilities, put up defenses, build up my stocks, and generally play conservatively. Within that framework, I've got a number of possibilities that lead to victory; the only question is which of them will come up first. Whatever the strategy, the appearance of Tubular Bells is always beneficial; as opposed to the appearance of a win condition card (All-Elemental Attack, Residence of Gods, Redesign, Battalion of Fear, or Bank), which may or may not be helpful, depending on whether or not I'm ready to win with it, or am in a position to eventually win with it. Other supporting Rares might also show up and prove useful; but I find that they tend to be situationally useful, whereas Tubular Bells is inevitably useful.
The trick is; unlike Uncommons, there aren't enough generally good Rare cards out there. Most of the Rares are really only worthwhile if they happen to fit into your strategy; having high costs, mutual benefit/malifice, or specific keyword requirements. Many of them, when they come up in your hand, won't be immediately useful; so they'll just sit there, and you'll wish you'd gotten something else. You might build up to it over a period, and eventually find some use for it... but in that time, you could have been doing other, better things, making the decision suspect. By contrast, there are a lot of generally good Uncommons, and you'll need to carefully balance these against those Uncommons which compose your main strategy... but as for the Rares, the decisions are a lot more obvious. I'll restate my original point here; unless you're running a single-color deck, Tubular Bells is a no-brainer. That's a little too good, if you ask me, but there you have it.
Oh, and lest I forget; it's entirely possible to win in less then 20 turns even with a slower deck, like Alliance. This usually happens when I fight one of those fast-paced Destruction decks you're talking about; if their cards aren't perfectly aligned, they won't immediately beat me with their modest starting resources, won't be able to put up a defense after running dry, and then I'll take them out quickly with my own modest offensive power as they founder.