Originally Posted by Warrrax
You want to save your IPs. They rotate the free champs every week, so play them all in practice games vs bots to see how they all work.
After a few rotations, you should have a decent idea what champ you like. Do NOT unlock a champ that you've never played! You may not like them and theres 20hours of gameplay gone. Dont rely on guides either because they are likely outdated.
This isn't bad advice, per se, but it fails to account for human nature. The first champ I unlocked was Xin Zhao and I had an idea I'd like him already from a few things: 1 - I like Jax's play style (I got him free) and I wanted someone like him but better 2 - Xin was consistently kicking our asses when I played against him 3 - He looks awesome! I have not regretted that purchase.
After that I unlocked Garen without having played him, but only because of reason #2 above. As it turns out, his playstyle is significantly different and, to me, quite boring. I regret unlocking him.
With those mixed results, I've decided to wait before unlocking my next champs. I am glad I laid out a little IP early and got one I super like, but that was pretty lucky. I'd suggest maybe unlocking some cheap ones that people consitently recommend (Annie, Amumu, Kayle, Yi, Ryze, etc) if you MUST spend those IP. Otherwise, wait till you get someone awesome in the free rotation and unlock them.
I personally and hoping for a few to try this week: Shen, Akali, Shaco, Udyr, Mord, Pantheon, Sona, Malzahar. Last week I got some I was interested in and didn't really like any of them enough to buy so it worked out.