In terms of reliability, costs? In the case of LocalBitcoins both with the use and without the escrow service.
If security if a premium, bitcoin-central.com. They are the only one fully compliant with the European legislation (bitstamp, despite being based in Slovenia, then in the Eurozone, operates out of the Eurozone since their account is in the UK). Plus, transfers are free.
Now if you want a nice looking website with usability in mind and would like to trade with powerful protections against loss, use kraken with trailing stop. Their fees are bigger so if all you want is converting euros to BTC, stick with bitcoin-central.
There is also the matter of liquidity. Here, nothing beats Bitstamp. Liquidity means the price will change more often so if you buy at market price, this is useless for you. It is only interesting if you buy at a fixed price.
And of course, there is still virwox.com if you positively want to take advantage of a quick drop in price which is worth the 10% commission
So, again:
- simplest, least expensive, and most secured: bitcoin-central.com (also the slowest if you don't convert on evening European time, since they operate a manual check)
- simplest, least expensive, and more chance to have your BTC cheaper or more expensive: bitstamp
- sophisticated and slightly more expensive: kraken
- fastest and most expensive: virwox.com
Hope this helps
