What, of all-time?
Either Rollercoaster Tycoon 2 or SimCity 4. It's a shame they don't keep time but it's got to be thousands of hours, up to ten-thousand maybe even. Have been playing them consistently since release 13 years ago. The only other contender for the title would be Anno 1602, but that one's definitely third place.
And no, none of those hours are wasted. Maybe a couple on SimCity when it crashed and I forgot to save. 







