I'm a pre-retiree who has camped in FL, RGV, and AZ. I haven't experienced "high season" yet as a transient RVer, but I like having the RGV as an option given how full the other areas get during peak season. Once I ultimately retire, I would like to come back to MN in April, instead of in January to start another grueling tax season.
I ride my bike everyday so access to bike trails or lanes is a key attraction for me. On my first visit to Harlingen, I was chased by an aggressive dog right outside the park (Lakewood RV Resort). It was a terrifying experience. One my second visit to the Valley, I stayed at Victoria Palms and was approached by 3 aggressive dogs who crawled under their fence...this right near the park on a walk back from Subway. I called the police after I got back to Victoria Palms, drove my car back to the location and filed a complaint. Just a simple walk outside the park was fraught with danger as there are no sidewalks and it feels like a very rough area.
I like the parks in the RGV but would never feel safe walking or biking anywhere outside the gated community. It's a wild west kind of a feeling. In many many years of biking and walking in MN, I have never been chased by a dog.
For those who like biking, the river trail in San Antonio (Travelers World is great) is very good. In Mesa there are bike lanes everywhere and good biking along the spillways which have miles and miles of multi-use trails. The only official bike trail I could find in the Valley was in the State Park and I believe it is unpaved and sort of remote, but I'm not sure. I often take my bike in the car to good biking areas so that is a potential option for anyone interested.
Bottom line, I like the transient lifestyle especially when I read this thread and realize all of these areas have something good to offer.
For folks who love to play cards, pickleball, bingo, dance, etc etc, the RGV seems like a fantastic option to me. There is good shopping and dining along the corridor and occasional trips into Mexico to spice things up. And not everyone can afford $1,000 + month for their winter home. The Valley is much more manageable financially as others have pointed out.