Where is it smart to buy?
Bitstamp and Coinbase, I'd say. I like Coinbase.
I'm pretty new but could someone tell me why is btc-e always a little cheaper than Coinbase? I am signed up at both but just trying to understand. Is it because one btc-e is an exchange? But what exactly makes it "cheaper"?
Yes, BTC-E is a European exchange. They usually deal in larger amounts via wire transfer from your bank. Coinbase is great for US customers as you can hook up your bank and do ACH transfers (like when you get a direct deposit of your paycheck) so while they are not technically an exchange, they buy and sell but at a small premium. It's probably the easiest place a US-based customer can get bitcoins.