For Mario Kart 7, I'm a huge fan of: Lakitu; Bumble V, Wood (Wheels), and the Flower Glider/Peach Parasol.
For Mario Kart 8, I've been experimenting a bit, and currently, my Wi-Fi combo is: Morton; Sports Coupe/Circuit Special; Cyber Slick/Crimson Slim; Wario Wing/Waddle Wing/Gold Glider.
In Mario Kart 7, I really had no interest in flat out speed. I preferred higher acceleration and handling, because drifting was too difficult with, say, Metal Mario/B-Dasher/Slick/Super Glider. Also, with the abundance of underwater tracks (Wario Shipyard, Cheep Cheep Lagoon), or tracks with portions of underwater (Rosalina's Ice World), Wood wheels were a good choice.
In Mario Kart 8, I just went full out speed. Fire/bunny hopping made the game feel so much faster. Cyber Slick wheels worked well on tracks with less rough terrain (e.g. N64 Royal Raceway), and Slim/Crimson Slim wheels worked well on more terrain-y tracks (e.g. Mount Wario). However, I feel as if my MK8 combo is so tryhard-esque.