I still own lot of FF books, probably around 70% (without checking) of the original run and a couple of the later ones.
One of my faves was Armies of Death which carries on directly from Trial of Champions and has you literally raising an army to fight some random evil that I cannot remember. Crypt of the Sorcerer is another one that really stuck with me. Great book.
I'm going to single out Scorpion Swamp as the utter piece of crap that it is. It's far to vague in it's setting to keep my interest and the paragraph's aren't very descriptive.
I was a never a big fan of the Lone Wolf books but Way of the Tiger is pure gold. Assassin (book 2) is the best in the series, all other viewpoints are to be considered at the very least misguided and ill-informed or at the most, just plain old wrong.
Cheers