Greetings!
The LAX-SFO shuttle is scheduled with the A319, although A318's could be subbed if needed. By the end of August, Frontier will operate 47 A319's and 7 A318's (as well as 10 CRJ-700 aircraft through a partnership with Horizon Air to operate Frontier's JetExpress operations). As each aircraft has its own individual animal on the tail and winglets, you can probably guess that it's difficult to predict who will be 'escorting' you down to L.A.

Thank you for flying with Frontier- the employees here sincerely appreciate your business. I occasionally work the LAX-SFO shuttle and think the route has become a success - I'm glad to see that some of our readers in this forum have taken to our new service. ^
Cheers!