You get the constant change of scenery without the hassle, but without the net drop that almost all ptp courses seem to offer. I don't know of any net uphill ptp routes, but I'm sure there are a few out there. It used to be that a marathon was a 26.2 mile road race. That's not necessarily the case anymore. In that case, one of the big city marathons is likely the best choice, although even some of the smaller races are amenity friendly now.
Travel is also part of the experience now as well, as alluded to above.
Some strong-willed souls even try to combine a family vacation with a marathon. Anyone who has run a PR using this methodology obviously had plenty of room for improvement. Traveling to a distant marathon as part of a charity group is a growing phenomenon. In Training program and Arthritis Foundation's Joints in Motion program are two examples. In these programs, you raise money for the charity in return for a trip to the marathon.