I will say playing with GAF does wonders for your MK skills. I *thought* I was good at Mario Kart before joining up (and, for all intents and purposes, I was) but the GAF group is just next level shit.
I decided to jump into online worldwide for fun last night just to see how I stack up. Took 1st easily in my first 3 races. I got bombarded by shells in the first lap at first, and even knocked off the stage. Glancing over at my position, I expected 9th, 10th or even dead last. I WAS STILL IN 4TH! Easy to catch up from that. At GAF I would've hit 9th place easy after that.
TL;DR: Play NeoGAF Tourney, git gud.
I'm actually kinda surprised at how well I can hang with GAF. I mean sure there are some folks that are absolute monsters for how early it all is, but I think consistently holding 1st - 4th place for multiple laps and closing out quite a few races in the top 4 is weird given how good everyone else can be in the GAF groups. :lol