Get both.
The pros/ cons of both setups will go around all day long... and than some.
I have the WARN (it does effect AP angle a little) but you can push dirt/ rock out of the way or slide over things with that bumper. I've seen it done. The multi-mount gets hung up in some situations and in some cases has bent the cradle. I've seen that happen also.
Now, if your looking for a "solves all" answer, get both, esp. if you off road by yourself (not a good idea all of the time), but you can winch from both sides if needed. To have to change out a winch when your stuck really sucks. Esp. if you are on some type of "V" situation and bumpers are already bottomed out. How do you get a winch in there now? In many cases (Moab), if you need to Winch, you can't get out of your truck to winch anyhow. Soem of the climbs/ shelves, require you to stay in your vehicle with the brake pushed through the floor boards.
To have to pull a winch off the back and put in the fron would be a pain.
i though you posted a screamin deal on one of those WARN bumpers already. for that price, I would buy both.
My "next project" is going to have both for sure. But they will both be integrated into bumpers.
good luck,
Tim.