If you want to get that killer Opeth tone, get a 5150. I have one and it just kicks ass! Especially if you like scandinavian metal because they all seem to use the 5150 (ex. In Flames, etc.) The 5150 has tons of gain and just kicks ass. The Mesa is great too but way too expensive. You can get the Mesa sound with the 5150 for 1/3 the cost. I picked up a 5150 head used in excellent condition for $400! Stay away from the Blue Voodoo. If you can't get the 5150 or Mesa, then I would recommend either a Marshall JCM800 or a Laney GH100L. They rock too but give you more of that British sound. To push them over the top (like the 5150 or Mesa), you will probably need a distortion pedal. Hope this helps.