Goku wins. 10 years of training even in peacetime is a huge amount for Goku. Considering from the very start of Z till the outset of the Buu saga was only like a fifteen year period and the massive progress he made there there is just no way I could imagine that he wouldn't get several times stronger. There were obviously extenuating circumstances but even in times of peace Goku has shown remarkable growth.
The five year period post-Cell seen him get many times stronger with no specific motivation. Those who are arguing that he could only achieve this through having such a unique training environment are forgetting his instant transmission, Goku could easily instant transmit there still to train with the likes of Pikkon, whilst having powerful training beats like Vegeta and Piccolo to keep him motivated. He has access to Capsule Corp through Bulma and all the technology he could ever need to aid his training.
Goku has been proven to display a similar level of Saiyan pride to Vegeta and there is no way I can see him accepting anyone else even his own son being stronger than him for long. The fact that Goku matched an admittedly relatively unskilled Uub, whilst only in Base form at the end of Z confirms this theory. When you add in Goku's far superior skill, resolve and ability to pull out a win in just about any given situation I just can't see Gohan winning this.