Flying J is on my list of good places to stop. With a gas MH and toad I find the RV lane to have a definite advantage, propane is convenient and I have always found the facilities clean. That said, often I have found that Flying J shares the offramp with other large fueling stations, and a quick drive around before pulling in finds the other stations to be either less crowded or have easier access. An example: Traveling on the I-5 in California at the intersection of the 12, North of Stockton, The 76 truck stop has much easier access and egress than Flying J across the street.
As for price or loyalty clubs, I look for convenience, even a dime a gallon becomes less significant when added to the cost of a two week family vacation. OK, a dimes a lot, but the difference is usually pennies.
JMHO