I've mined most of the alt-coins, and while they're fun from the technical standpoint, I don't see them being useful for anything other than a means for experimentation and currency exchange speculation.
If bitcoin proves to have some yet-undiscovered major flaw, I suspect a new fork would be created rather than anyone flocking to an existing alt-coin.
The currency exchange speculation is my primary interest in other alt-coins. This is from the perspective of easier mining which may make it more conducive to garner a higher number of alt-coin to then trade for BTC.
I doubt any other virtual currency has a better chance at taking off than Bitcoin right now.
I agree that BTC has the highest chance of success currently but I also think that the possibility for up to three major players in this space exists. That is not based on anything more than a "feeling" but I see it as possible, especially if the confirmation times of other alt-coins cause them to become more attractive to retailers.