In the end, it's not too important. I'd say Vegito is more popular simply because he's been in a lot more. If Gogeta was in the main series, then who knows--maybe he will be. Goku using Kaioken on top of SSJ was used in a filler arc when he fought Pikkon (so it wasn't canon). Guess where that turned up again? DB Super. That opens the doors for non-canon things to be used, like Gogeta. Sorry for being a dick; years of GameFaqs can do that.