Malak was an angry idiot. Revan wasn't. They're not similar at all, really. At least, if official K2 canon is to be trusted.
And when one tries to ascertain wheter Revan was/is/will be "evil" or not, it's rather good to actually try to see the picture for what it is. Revan fell to the darkside at a certain point, true. Kreia later says that few know the difference between a sacrifice and a fall, and so on it goes.
The discussion becomes one of motivation rather than action, it seems.
Here's a few things to think about:
1) Revan did leave important infrastructure (not only factories and such, but infrastructure vital to the republic) behind. Malak didn't in favour of destroying entire planets at a whim.
2) Take the star forge: Revan only saw it as a (temporary) factory. Malak didn't agree with his master, on both counts. Anyone who's played K1 should know this.
Ever entertained the notion of that the coming war or whatever Revan saw might not be won with a stagnant rebublic? That normal rules of engagement need not apply, since applying them would only doom the galaxy(omg!!!) and so on and so forth? Perhaps Revan only did what he did out of necessity, instead of simple conquest (Which was obviously malak's prime motivation) and evilness?
At the end of the day it's anybody's guess, true, but all evidence seems to paint a Revan as a hopelessly pragmatic boy/girl, and not much more.