Head comparison..

I would obtain my favorite cab and bass. Then I'd plug the cab and bass in to the first head, power up the head and play the bass and adjust the settings on the head until I got a good feeling for how it sounded. Then I would repeat that process for the other 3 heads in question.

How would you compare them?

 

Sorry, I couldn't resist

 

D800 - Some Mesa flavor, clean sounding, can overdrive, great mids, clear lows, clear highs.

WD800- more color to it. Lots of tube influence, warmer sounding, has that tube amp at higher volume feel, not sure about the overdrive content, but it sounds fantastic if you want the tube amp feel without the hassle.

TH500 - Heavily colored, lots of overdrive, lots of thick mid-range. Decent highs, lows are there, but not very clear at mid volumes and up.

EBS - I tried a Redimar head once and remembered a lot of high end content. It was bright and decent sounding, but it did not make me happy to play it. The bassist in Neon Tree has used EBS and the song "Animal" is dead on to the EBS tone.

Think about how much of your bass tone you want to shine through the amp. I have the Mesa D800 and love the fact that I can hear a lot of what my bass truly sounds like. I don't like fighting the heavily colored bass heads.