Good second planes:

-Most any stik (GP Big Stik or Easy Sport, Hangar 9 Super Stik/Ultra Stik, TT Tiger Stick) except Goldberg Hot Stik/Wild Stik - too aerobatic
-Low wing sport planes like the Goldberg Tiger 2, Sig Four Star, World Models Sky Raider Mach II, Hangar 9 Pulse XT, Seagull SpaceWalker II
-Semiscale trainers like AT-6 Texan, PC-9, T-34 Mentor

If your dad is ready to tackle a long building project, there are some nice kit-only choices out there like the Sig Mid Star and the GP Rapture 40.