Definitely buying.

When you wanna get into mining you need an ASIC hardware, which is expensive.
It is very unlikely that you will ever break even, because ordering it now (from Avalon, Butterfly labs) you have to wait for months. And the network Hash Rate is drastically increasing making your investment less and less profitable every month. ASICMiner is the only company that delivers ASICs quickly, but again, their hardware is for professionals and you'll need some skill to set it up.

In my opinion the best solution (if you really want to get into mining) is to buy ASICMiner shares. You're getting profits from everything friedcat (company owner) mines with his 22 TH/s machines and you get your cut from every penny he makes on ASIC hardware sales, so you're not all dependent on his mining network percentage. Profits are divided equally on every share (there are 400,000 total shares, ~230,000 still belong to friedcat).

Why shares, not hardware?:
1. You don't need any professional skills.
2. You don't have to spend your time taking care of it.
3. Your money is liquid, you can sell your shares with a single click (and you can't do this with hardware).

Even though buying shares is a risky business, I believe it is fairly safe compared to investing into mining hardware not knowing how to deal with it.