There's not $10 difference in the two mowers. I have a Craftsman 18hp that is pretty much the same one you have listed - the one you have listed is just the new version. I have not had a lot of trouble out of it - other than blowing fuses for no apparent reason, and awfully short battery life. Deck belt is not very long lasting, Deck engagement cable broke last month - part has been on order for two weeks.... still waiting.
I actually am pretty hard on the mower.
If the same price - I personally would buy the Cub if presented with the same choice. Some nice features on the Cub that the Craftsman doesn't have. I don't know that the 13 guage vs. 12 guage (12 is thicker) will make much difference unless your dad is going to mow rocks! The deck cleaning system on the Cub also sound convenient.
What nice gift for your Father, either way!
I used to be the set up man for a tractor and implement co. That means, I assembled the stuff. The cheaper cubs, at that time, were yellow MTDs. The expensive ones were as good as anyone made, but the cheap ones were about the same as anything you can buy at Lowes. Not to say they're not worth the money. One thing I checked on when I bought a new mower was the transaxle gears. A lot of them are plastic. You can look at the transaxle and get names, spicer etc, and numbers, and find out which are plastic or metal. BTW, I bought a huskee, a tractor supply brand.