Fifth wheel or travel trailer?

5th wheel is absolutely not for you.
BLM, boondocking, nat forests etc.
Used to tent camping and upgrading for some creature comforts, not looking for a home on wheels. Short trips.
Smallish TT or pop up or truck camper seems more your style.

Depends how much room you're looking for. It's space and amenities vs how far off pavement or how narrow a forest road you can go down.

If you're looking to dump the camper on asphalt and hit the back country for day trips in the pickup then you could upsize the TT for more space.

Your current truck could work with a smaller RPod or similar. But living in Denver area you will not like the towing experience. Same for most any gas motored truck. If your buying used, look for a gently used diesel, and forget 2500 series instead get a 3500 SRW. Mpre towing capacity, better resale value all for the same money. Especially if your considering a future fifth wheel and dont want to upgrade tow vehicles again. A peoperly equipped 3500/350 can handle most fifth wheels up to around 32-33 feet. If, and I would suggest first a TT you start that way you can safely pull what you find. But, remember start used and start smaller. Towing can be a big learning curve. Same for the RV lifestyle.

I don't have an adequate TV for anything substantial. Currently a 2012 GMC Canyon 4x4 with 1080# payload capacity. It is my wife and I with a year-old baby boy. Have backpacked and tent camped (car camped) for years and the wife is wanting more creature comforts for her and the little guy. We like state parks, boondocking, national parks and BLM land. Will mostly be 3-season camping for 2-4 nights at a time.

I could maybe tow something like a Rockwood GeoPro with my current truck but otherwise I am looking to upgrade to a GM 2500 gasser.

Yes.
Start used.
Start small.
Start cheap.
What is your intentions for use.
What do you have to pull it with?

It is what you believe fits your family. We choose a TT. We like the size and the walk around bed and it fits our TV. I pray you are happy with whatever decision you make.