Some quick checking shows Billyland has an A+, BBB rating, but I couldn't find one quickly for Landcentral.
I found some concerns on Sitejabber.com for Landcentral. I didn't dig through the reviews though to see if they're legitimate concerns. Billyland only has 2 reviews there, but both are good.
Using this search string in Google pulls up other outfits (landwatch, landandfarm, landsofcolorado, etc.): land for sale in colorado.
Are you buying just land, or land and property? I'm familiar with purchasing houses combined with land, but haven't purchased land only before. There are definitely some things to watch out for if a house is included, but I suspect the land-only purchase process is simpler.
I recall you saying you want to park an RV on the land which sounds great. I highly recommend checking the appropriate county zoning to make sure you won't run into any headaches living out of the RV post purchase. I found some other things to watch out for at
Axle Addict.
I've seen some land for sale on Billyland that wasn't accessible all year around, so be cognizant of that as well.
How exciting....happy searching!!!