My best five true acheivements are from UFC 2009 Undisputed. I am a MMA nut, go figure. lol. A lot of people I know who played the game played through one career and some online matches and that's it. Many traded it in after that or they rented the game. So that's probably why the game has a lot of achievements with a high TA ratio. So it's not necessarily indicative of how hard the achievement is. A high TA ratio could also mean that gamers couldn't be arsed to go through the effort to get the acheivements. A lot of achievements are rediculously tedious and do nothing to add to the enjoyment of the games.
This is my list.
And for the record I didn't get Sceneit? for achievement whoring purposes. I actually enjoy those kind of games. Going for that 1000/1000 did get tedious though. All on the Line (10 ranked wins) was easy for me though because my memory and big button pressing reflexes are the pwnage (lol). The majority of Sceneit? players online already played through the game to death offline (to the point that the game kept repeating questions) so they pretty much know the majority of the answers. But I was still able to go undefeated on Xbox Live (and after getting the achievement, I retired. Since I see no point in playing a quiz game where I already know like 90+% of the answers by heart. That's not fun) in large part due to my excellent memory (I memorized the answers better than everyone else, I consider that an achievement. lulz) and uber-big plastic button pressing reflexes.