From my limited experience I can tell you this:
The quality of the fit of the pieces varies not specifically between brands, but between models.
All the Monogram/Revell kits I have seen or built, lacked details. Also some parts are too 'fat' and models too big maybe. Sometimes it takes a small saw to detach the parts from its frame. Normally they fit okay though. I hate the 'silver' plastics though.
All the Italeri kits I have seen or built, are more detailed, but often wrong details (random even). I think Italeri has lighter parts compared to Revell which is great if they fit. If not you have a problem.
Tamiya, I'd say one of the best around, but their limited selection of aircraft kits are mostly more expensive.
Heller, my limited experience with this brand has been disappointing. I liked the way the plastic 'feels' though.
Still there are some other brands I have not mentioned, because I had little or no experience with them.
Regarding paint, for enamel paints I think Humbrol is the best. Revell paints are mostly too thick. Although I've been using mostly enamel in the past, I have bought a lot of acrylic before I ceased my modelling activities, because they are better for airbrush.