We stayed in Mission for a few weeks last winter, our first time there. We enjoyed it, lots to do, the only draw back is the RGV is a very busy place. Lots of traffic. I'm not familiar with the parks you mentioned. We stayed here
RV Parks South Texas, Bentsen Grove Resort for Winter Texans in Mission Rio Grande Valley
an older park but we liked it. Nice folks and it was far enough from the freeway to avoid the traffic noise.
Be sure to visit the Bentsen Rio Grande Valley State Park. Bring your bicycles if you have them, no cars allowed in the park. If you don't have bikes you can use the park shuttle bus. Great place for bird watching, they have blinds set up with feeders and water so there are lots of birds to see. Also, take a tour of the Old Hidalgo Pump House, very interesting.
While your traveling through Texas be sure to take advantage of the excellent State Park System campgrounds. We stayed in 7 or 8 different Texas State Parks last winter and there isn't one we wouldn't go back to.