It completely depends on what conditions you will be riding most, if its going to be lots of down the line sailing then you will benefit more from the acid whereas if its more gusty crumbly onshore conditions then the evo would be better. If you arent all that experienced with wavesailing then the evo would also offer more as its a more forgiving board, although it can still be pushed hard.
You will just have to weigh up what your skill level is and what conditions you usually sail in and bingo you will find your board
Try demos of aswell if you still cant decide.

Go for the Acid! Its faster than the evo and turns better; pure wave board!

Very happy with my Acid 74 as a high wind board. Seems to take 20kts+ to get it going, but once there, it's sweet. Never sailed an Evo but I think it'd be planing a lot sooner.

I bought my 88 acid 3 seasons ago, took a while before I really got the feel for it. It is a very fast board and jumps well, you can set it up to be very slashy if required or stiffer for larger sail/lighter wind.

I used it as my only board for 2 seasons then got a Fanatic freewave 96 as my 'light wind' board. The acid is great when there's 22Knots + and I always use it if I can, but its not much fun below 22Knots

In summary it's a Fast,loose,jumpy, high wind board with nice graphics.

(think about the Fanatic wave or freewave too)

Sinker, how do you set up the Acid to be stiffer for bigger sails. I assume you move the fin back further in the box, but do you do anything else, eg mast track and straps? I tend to be too impatient or lazy to play around with tuning much, probably to my detriment.