I'm sorta a completionist but not an avid one. I still pick and choose so stuff like X, X-2, and XII will probably never be finished completely cause I reach a point I feel its irrelevant and all about posturing. Still there are some games that bring it out of me.

VI and VII are the easiest. Collecting every item and maxing out every character is pretty easy as long as you have a good head on your shoulder. Granted a few items are tricky (Behemoth Horn weapon in VII or the StoneBlade in VI come to mind) but a few playthroughs and actually exploring multiple paths will net you most of the stuff. Even the optional bosses/slash super random encounters are not too difficult if you tweaked your party right.

Tactics Advance gets the award for most difficult. Mostly cause item rewards are partially randomized and several items were designed to only be easily acquirable through connectivity play. This becomes an issue if you don't have people to play the game with... not to mention the mission system is set up in a way where screwing up an wasting an event item sometimes leads you to waiting forever for the mission you originally acquired it in to pop back up. This is all climaxed by the fact that abilities for job classes are learned off of weapons and equipment. I was 30+ hours past beating the main game before I acquired the item that game me Firaga. I've still only been able to master one job class and I'm over a 100 hours into the game. I'm also only two missions away from getting Cid and doing the Judge story arc but I can't get the damn mission that gives me Black thread to pop up... Grrr