Can’t help you with Rixeyville, never been there. Based on the map it does look to be further away from the park than McGaheysville. But I grew up about 30 min from McGaheysville and there is nothing to do besides the park (unless you go to Massanutten). You do have pretty good central park access, and it would put you closer to Harrisonburg for more food options and any other activities. However it puts you on the other side of the mountain and quite a bit north of Monticello. If you want a more central location between the park and Monticello, I’d have to suggest Waynesboro. The downside to Waynesboro is that it is the southernmost entrance to the park so you wouldn’t be centrally located. But, you would also be right where the Blue Ridge Parkway meets Shenandoah National Park so you could explore that as well.