I routinely stop for diesel at all kinds of truck stops, and have found them all to be welcoming to RVer's. I haven't found any other than Pilot/Flying J that offer discounts; however, it seems the Pilot/Flying J prices have risen so much that I can beat their discounted prices at many other truck stops.
Parking spaces are generally not an issue, but I don't know about dump stations as I have never wanted to dump at a truck stop.
I prefer truck stops because there is plenty of room to get in and out; however, be aware that the diesel pumps and area around them will most likely be an oily mess. Just something I put up with.