Not based on specific Rhodes 19 experience, but general experience is that a loose footed main is easier to see and adjust the amount of draft for the lower portion of the sail. (Outhaul adjustment.)
Before I went and bought new sails, I would consult with the class association to make sure there is no prohibition on loose footed mains, or if there are any class legal lofts for sails.
http://rhodes19.org Whether you wanted to race or not, this decision could make it easier to sell the boat later if someone were a racer and wanted to buy it, they'd already have class legal sails.
For example, I know there are 2 class legal lofts for both the Flying Scot and for the Force 5. I chose to buy a non-class legal sail for my Force 5, considering I didn't have a racing fleet at my lake. I think a local club would still let me race with them if I decided to make the trip, but it would be nice to have a sail from the approved loft, which is also considered to be the fastest sail. Just didn't feel like getting spendy at the time...
Ahhh, here it is in the rules, section RB 21.01.03:
"The full length of the luff (except when reefed) and foot of all mainsails shall, when
in use, be attached to the spars by having the bolt rope or slides run in slots in the spars. No loose footed or miter cut sails shall be used."
http://rhodes19.org/class-rules/rulebook/
So, yeah, no loose footed mains are allowed for a racing Rhodes 19.