[Si Coe]

I got faster when I ditched the 5.5 and 6.5's and went to 10.5 instead. More power is a hindrance if you can't control it.

As for what class to go for - that depends on the club and whats popular. Generally 2wd is more popular and many clubs will get 3-4 heats of 2wds to 1 heat of 4wds. That tends to mean that the racing is closer in 2wd which is better for learning.
Other clubs just lump all the buggy's together. If thats the case, a 4wd is a major bonus because they do lap faster.

In terms of driving experience I'd say its a tie on a high grip track - I've driven 2wds I've loved and 2wd's I haven't, and that same for 4wds. A good 4wd is more fun than a rubbish 2wd and vice versa. On a slippery track its a matter of personal preference - some like the control that 4wds retain, others enjoy the challenge that 2wds become....