I'd start by figuring out what you want to do with the RV. Weekends, full time, long time (trips of 1-6 months at a time) vacations (2-3 weeks). Then talk with whomever is going with you and figure out what you'll be doing while you're using the RV. It could be sightseeing (go to Mt. Rushmore and back home) or it could be in depth travel (go to Sedona and spend 2 weeks looking around visiting places within 100 miles, then moving 200 miles and doing it again for that area) or it could be going to Grand Canyon, Zion, Petrified forest, Tombstone, Nogales, and Albequerque (a whirlwind trip of many places all for 3 hours each).
Figure out what you plan to do in the next 5 years and what you'd like to do in 10 years. Here's where I differ from many. I want to buy ONE rig and keep it for a fairly long time. I don't want to buy a rig this year, use it to find out what I like to do and then sell it to buy another one. Then decide what I really like, sell #2 and buy another to do what I want. By thinking it through and planning ahead you can make a pretty good guess at what kind of rig you should buy.
If you take longer trips you'll most likely want to tow a vehicle for sightseeing, groceries, entertainment, etc. Will you need to carry 3 kids and 2 parents? Or just 2 adults? The kind of toad (tow vehicle) you get will need to accommodate the people you plan to take. You'll then have that check point on your list to look at hitch capacity. Some are as low as 3500 lbs, some as high as 10,000 lbs or more.
The RV will need to be powered to tow the vehicle. The RV will need to have sleeping and eating accommodations for that many. Will everyone be happy in a small space? Does someone need to have more space? There is no sense in buying a 28' rig if the other half is claustrophobic inside while you're looking at rigs. You may need to buy bigger just so that person is comfortable with the space available. Are you going to use the rig out west where there are mountains? Or in the east where a freeway overpass is considered a high spot? Location of travel will sometimes dictate size of engine. While you can crawl up every mountain in 2nd gear with the gas engine howling next to you...... do you want to?
What level of comfort do you want? What level of quality do you want? What speed do you want to travel? These are money questions. The more comfort, quality and speed all cost more money.
There are more questions than this, but this will get you started down the right path. When you go to the show take your camera and a notepad. Write down which rig, make, model, and size and take pictures of things you like and dislike about each one. Write notes about things not obvious in picture. Notice the heating system, water system, water heater, sink size, clothes storage, crawling over someone to get out to the bathroom at night, where would the coffee pot go, does everyone have to go to bed when the kids do because the living room becomes a bedroom, and so on. Write those things down. Put those notes in a 3 ring binder for review later. Look at high quality and low quality. Look at bigger than you think you want and smaller. And talk. Be honest. Are you planning to make sacrifices now that you'll regret later? If you're going to buy a rig with the idea that you'll get something different "on the next one", then why are you buying this one that you know you're not happy with?
And yes, few have unlimited money to buy everything that they want. But by thinking thru the process you'll be much more likely to buy something that you'll be happy with. At least that's how we did it. And as a last thought, look at the new ones at the shows, but plan to buy used. You can save a lot of money buy buying a 3 year old rig rather than a new one.
Ken