I'm not sure why people complain about Test of Faith. I got that one on my first playthough. It's easy, considering that you can a) melee, and b) just run away. Bobbleheads in FO3 was also not bad... most were close to locations necessary for other achievements, so I just got them along the way.
The worst achievements ever for me were The Final Instance and The Last Remnant (closely related achievements) from The Last Remnant. They required excessive grinding in a game that was already long and dull, and the bosses were mind-blowingly hard. I keep all of my games- never trash or trade? but I very much considered setting fire to that disc when I was done with it.
Also, Compulsive from Infinite Undiscovery. Truthfully, I never got that one. I should have, but somewhere in the hundreds of items, I must have missed one. Dozens of hours of work for nothing. Goddamnit.
I don't play Square Enix games any more. Guess why.