Brands do make a difference. For an older model, a Winnebago/Itasca is great because the website has old brochures, wiring and plumbing diagrams to help you learn about the RV. Winnies also have the fiberglass roof. If you are only spending $5000 or so it will be more difficult to find one that is in usable condition.
I agree that the 24' length is the way to go for 4 or 5 people. Look for one with an overhead, a couch and a dinette if possible. We are traveling right now with the grandkids and I love our length (22') but it is a little tight. We have had 2 couples and 2 kids in it though and as long as you are friendly it is doable. The dinette, the jack-knife couch and the overhead queen makes sleeping for that many possible even in just a 22' rig.
NADA on ours used is around $15,000 to $18,000 mostly because it has about 40,000 miles. Everything in our works great but it is starting to look ragged on the outside. I have put Enternabond tape on the edges and roof to keep it from leaking and the tape is getting ragged looking. The decals are peeling etc. We are DIYers so we have made some upgrades and we take care of it because we love using it. It is very easy to drive being so short, we have never upgraded the shocks or any suspension. The Ford V 10 engine is very reliable after about 2000.
I knew nothing about RV's when I started researching. I found looking at photos and floorplans on PPL and watching their selling prices helped. They don't have much in the 24' size now but the site is
PPL Class C Motorhomes.