We were at both Banff and Jasper this past summer on our way to Alaska. Here are a few things to think about. Banff is only an hour or so from Calgary, AB so many of our Canadian neighbors go to Banff for R&R as well. If you are going, I would encourage you to make a reservation there as soon as your dates are firmed up. Tunnel Mountain CG is hilly, and we found ample distances between rigs in our area. The shower and bath facilities were good, we used them daily. The town of Banff is very touristy, crowded at times, with very limited parking for RVs. As you enter Banff (the park), you will need to purchase a national park pass. At the Tunnel Mountain CG, there is a city bus stop that takes you right into town. If picked up at the bus stop in the CG, the bus is free on the way into town. Taking the bus back to the CG requires a fare. Go into town and enjoy the shops, restaurants, and the people. Consider a ride on the Banff Tram to get an elevated view of the area, see the famous hotel, walk to the Cave and Basin to see where the Canadian National Park System began. Lots of things to see and do.
Suggest you also take the Icefields parkway to Jasper NP. You can stop or stay at Lake Louise along the way. Beautiful scenery, and we saw lots of wildlife on the way. You will pass the Icefields Centre along the way. It is very worthwhile to stop and arrange for a trip on a "sno-coach" that will take you out onto the Athrabasca Glacier across the road. We also arranged to go out on a overlook over a gorge, a mile or so down the road, but did not enjoy it as much and didn't believe it was worth the price of the ticket.
We stayed at Whistler's CG in Jasper NP, with full hook ups. I don't remember the quality of showers or facilities. While at Whistler, we had a cow elk and calf in our immediate area visiting quite often. Whistler's is quite different than Banff. Banff is more touristy, while Jasper is more akin to natural beauty. Yes, you can drive your rig into Jasper (the town) for shops, restaurants, etc. and there is ample parking in town.
Finally, as noted by another, before going to Banff, if you have time go to the Head Smashed In World Heritage Site. It is amazing to learn how the Early People used logic in their buffalo hunts.
Have fun planning your trip and I wish you the good times we had on our trip.