Free feeding will often lead to pudgy cats. In the wild, they don't have free access to food, they have to hunt, be active, wear off what they've eaten.

As for food, this link is great for learning what to look for in cat food:
http://www.petfoodratings.net/cattable.html

Read some low rated reviews and some high rated reviews. In the wild, the only grains cats ingest are those eaten by their prey and in that stomach. Cats have no way to digest grains on their own. They are obligate carnivores, meaning they must get all their required nutrition from carnivores, nothing benefits them from vegetation. I feed grain free, have done for 3 years now. Those slightly overweight slimmed down nicely with no problems at all. I use Taste of the Wild, the Canyon River formula. My cats aren't keen on the Rocky Mountain formula.

Dry, wet or mixed? I mix. I learned the hard way, after 4 cats developed CRF, and much research, that cats rarely drink water. Again they take in most of the moisture they need from their prey. So I use canned as well. Sparkle was diagnosed with early strage CRF over a year ago; that is when I researched and started using a mix of dry and canned. She has slightly improved! So I keep it up.

Just as for humans, eating properly is part of prevention. I'll pay the extra for a high quality food, and save on the vet bills and heart ache. At least, that is my plan, lol!