I did my first playthrough without a guide. Most of the marks aren't too difficult to spawn. I wasted quite alot of time on Lindwyrm i remember because the gentlemen who posts the bill tells you to look in the the Highlands but he appears in the garden of lifes circle which was pretty misleading. Maralith was a bitch to spawn too. I got most of the marks but didn't beat Omega, Ultima Hell Wyrm, Yiazmat and maybe some others. I knocked the out of Zodiark though.

I think playing without a guide is the best way to enjoy the game. There's so much to discover