This has some different answers.
Here is my view:
Most Amps these days take XLR…You can buy 1/4″(TRS) To XLR cables from most music places and this imo is THE best way to connect. or TRS to TRS if available. TRS and XLR will have the best sound qualitiy to them.
You CAN go Rca to Rca but i dont really reccomend it. Any RCA cord will have sound degredation after 6′, and even more so at 12′.
Now this sound loss you may not really recognize on your home system or on a small PA system, but I can totally hear the difference when i do BIG shows, and thus refuse to use the RCA for anything else other than plugging into the house mixer.