Well, I'm a newbie so my opinion may change with time. To me, there are two kinds that I like. The first kind has lots of simple riddles and things of interest to my 12 yr old. The second is one that takes me someplace new and interesting (for me). For both, I prefer scenic terrain. Tough or easy to get there is fine. But I don't want to spend hours looking once I get there. And I don't want to leave after a tough climb without finding it. MOST IMPORTANT is not to make the terrain annoying (avoid places like mosquito infested swamps). Sea side, moutain top, river side, in the woods, in the desert, all of these are good.