It's pretty much all about personal preference & which one looks the best to you. They don't do much for accuracy improvement or for recoil reduction. The slant style is the 'classic' Russian AK look.
Mine is the Tapco Razr....
I'm thinking about getting the rpk style muzzle break it looks awesome
I put that on my WASR after I cut off the muzzle nut. Figured it made more sense than the slant brake and I knew I'd get laughed off the range if I got an A2 birdcage. Tapco's is cheap and looks good.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together. You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek