Fishless is the only way to do it as far as I'm concerned, and I feel very strongly about it. How long the cycling process takes varies extremely widely and depends on a LOT of variables--people may think that it takes longer to cycle without fish because they don't feel the need to heat or aerate when fish are not in the tank, and forget that bacteria need heat and aeration to grow and thrive. Also, when people transfer fish into larger aquariums they bring decor and plants that already carry some beneficial bacteria, and for that reason the process would go faster.
Basically, I'm saying the process will go as fast as you let it, fish-in or fishless--however, because you don't have to worry about the welfare of the fish during the fishless cycle, you can add more aeration than you normally would and jack up the heat higher than you normally would to encourage the bacteria to grow faster. You can also add mature filter media or gravel mulm to speed up the process immensely, if you add enough you can complete the cycle in just a few days.
You also get a much better yield of bacteria from a fishless cycle, because instead of keeping your ammonia low, to about .25ppm, for fear of hurting your fish, you can keep the ammonia at 4ppm, so much much more bacteria is produced in order to consume this high amount of ammonia. This will make the bacteria colony more stable when you add fish, and you will be able to add more fish at the same time, ideal if you need to cycle the tank for schools of fish like pygmy cories and whatnot.
You also don't have to do as much work in order to cycle a tank fishlessly. Simply add 4ppm of ammonia to the tank, and test until the nitrite begins to spike. Then replace the ammonia that has been consumed until the ammonia and nitrite levels are 0 and the nitrate level has spiked. All you have to do is test, add ammonia, and providing you don't overdose your tank on ammonia (if you OD, you could kill the bacteria. In that case you would need to change some water to lower the ammonia level.), you will only have to do one water change at the end to get the nitrate level into a safe range.
Simple, easy, safe for fish, and you get a much better yield of bacteria. And I don't know, in my mind its just wrong to expose your fish to toxins when you could avoid it--if you've ever smelled ammonia, you know that it is not a pleasant thing to be around. I can't imagine constantly having to breathe in, drink in, and swim through ammonia water all at once. Yuck. Don't put your fish through that please, even if they don't get sick from it, it's just not a nice thing to do.