I use default. I am very picky when it comes to textures and while default isn't the best looking it's easy to look at. Massivecraft's causes a slight bit of lag, but worse than that it changes a few items around so when I look in my chests I can make heads or tails at a glance. I occasionally go on a binge a look up a bunch for the heck of it. It's always the same though. Either it changes too much or it causes lag.