Most of the truck stops i have seen as far as Petro, TA, Flying J, Pilot, and Loves have pretty decent showers. But I'll give you a few extra pointers. Flying J, Pilot, and Loves have some of the cleanest truck stops i have seen. Most people that work there are pretty friendly. Some of the smaller Pilot and Flying J's might be a little different. Internet-wise, Flying J, Pilot and Loves have the best quality internet. Both also have yearly subscription plans, which is a huge plus. I think the yearly subscription rate at Pilot/Flying J is $150 for 1 year subscription. And it does not matter if you park at a pilot or flying j, they are owned by the same company, all you have to do is connect to their outdoor enhanced network and log in on the website, connect, and your in.
Petro always has a decent restaurant, and TA is known for having full-service truck stops. both Petro and TA have laundry in almost all their locations, which you can now use a credit/debit card to pay for your washer/dryer usage. They are also decently clean as well.
If you choose to park in the truck lot, you may want to park on the perimeter of the lot, or snugged up against something. I have seen rv's park overnight in the car parking areas and not be disturbed at all.