It depends, whether I just want to breeze through the game, whether I'm playing as an Hybrid or whether I want to finish the game with maxed out stats.
For Quest For Glory I and II, if I want to breeze through the game, I typically dump everything in one stat: Vitality to survive longer as a fighter; Magic (or Intelligence, whichever stat gives more Magic Points) to cast spells more often as a wizard; Stealth for the thief because it is very time consuming to raise that stat until you can avoid fights in the wilderness.
When I play as an Hybrid, it's typically to complete every single quests and side quests in the games, so I go for Fighter + Magic + Stealth + Lock Picking, that way I can fight the sword master in the castle courtyard and also join the Eternal Order of Fighters without changing classes in the second game and the lack of climbing skill isn't a problem with the levitate spell.
Back in the days when I played the first two games with the intention of maxing out every possible stats for my classes, I usually dumped everything in the stat that was the hardest to raise in that specific game, or for that specific class, like intelligence for the fighter or strength for the wizard.
In Quest For Glory III, as a thief I dump everything into lock picking due to the lack of doors in that game and my paranoia of finding myself in an unwinnable state because my lock picking stat is not high enough, like it happened the very first time I played Quest For Glory II.
As for Quest For Glory IV, either I'm playing it wrong, either I'm not thinking with class specific skills when it comes to avoiding fights (or maybe I should stop pushing that combat difficulty knob all the way up to eleven) but I found myself dumping everything into vitality as a fighter because fighters gotta know how to fight and fighting was so dang hard in that game, especially against those cheap necrotaurs and projectile throwing enemies.
When I replayed the game as a thief, I dumped everything into stealth, thinking I could avoid those cheap fights that way, and immediately regretted not dumping it all in vitality when I saw the number of unavoidable (I think) fights present in that game and how useless stealth was at avoiding both mandatory fights and wilderness ones (even with near maxed out stealth, I was still triggering monsters all over the place.) Thankfully I did not make the same mistake as a Wizard and dumped everything into vitality, where it belonged.
It's been nearly two decades since I last played Quest For Glory V, so I can't really help with that one.
Post edited August 24, 2016 by blueskirt42