Under normal driving, the fluid does not need to be FLUSHED until seven years or 105,000 miles, whichever comes first.
AMSOIL ATF, Castrol Import Multi-Vehicle ATF and Valvoline Maxlife ATF are all multi-vehicle fluids that claim SP-III compatibility but are not OEM approved.
Also, you should also be aware that Hyundai uses a chemical tracer in the SP-III fluid. In the event that the transmission fails, a fluid sample is taken and if the fluid is not SP-III, you'll be facing an uphill battle.
You might want to wait until you are out of warranty (the fluid change isn't due until 105k) before switching to a non-OE fluid. The fluid may turn brown, but that's normal according to Hyundai.
11 Prius, 158K, ACDelco Syn 0w20
07 Accord I4, 122K, M1 EP 0w20
10 Altima 3.5, 40k, M1 EP 5w30
92 Previa, 167k, Chevron 5w30