MSSQL is Microsoft SQL Server ( http://www.answers.com/ms+sql&r=67 )

MySQL is Open Source SQL Server ( http://www.answers.com/mysql&r=67 )

I haven't looked at MSSQL for a long time, but I believe it's like ~$1,000 or so? MySQL = free

Still cheaper than Oracle's.

wow, why pay ~$1000 for something when you can get the better of the two [free]?

MSSQL is a little more powerfull database server, but it does cost money.

MySQL beats the shit out of MSSQL, but MSSQL is more secure..because well..no one uses it? lol

Well that is your opinion and im not going to argue... i personally think mssql is a strongly database server since it has stored procedures. But i heard the latest version of MySQL also has stored procedures, but im not 100% sure on that.

MySQL is starting to include transactions, etc. to be more comparable with MSSQL. PostgreSQL has been touted as being more like MSSQL, but I'm still a big fan of MySQL & never have had any issues with it.
Suppose it depends on your needs... If you're the McDonalds of the cyberworld you may want to research your needs of a database, otherwise MySQL (I would argue) may be best option since it is so widely used (you can always google query examples for it, that's for sure... and that's only if you can't understand the huge freaking manual)
MSSQL on the other hand charges $... and if you're the type to get on the phone with tech support, then you may actually prefer this option... that's the kind of thing you're paying for here (though, I don't actually know how their tech support options look, I'm just assuming for that kind of $ is should at least be decent)