I thought about other altcoins but I always come back to the fact that bitcoin pretty much nailed it the first time round. Technically its an amazingly "first stab" at something so fiendishly difficult. It ticks all the "need" boxes and people argue alot about the other stuff (whether anonymity is necessary (or bad) for example)
When you start looking at altcoins, you realize there is noting to stop them from proliferating, there are new ones springing up in bedrooms all the time, technology always makes things, even virtual "money", cheaper to make, so that's when you know they aren't worth investing in. Most will just be ways for geeks to use their spare gpu's no longer any use for bitcoin mining.
Altcoins will only succeed if:
a) bitcoin is found to have some fundamental flaw (unlikely since it hasn't been found yet)
b) err... .can't think of a (b). Perhaps the US government launching its own altcoin
If bitcoin goes down in flames because of government interference, no other current altcoin will jump up saying "I can succeed where bitcoin failed". Its bitcoin or nothing.