Isn't it a bit broad question, since the rpg's definition itself comes with character customization?
It's a fair concern, because many RPGs don't actually allow for any decisionmaking during character advancement. For example many of the old RPGs would just give you a new skill automatically when you reached a certain level. I don't think that is very interesting personally. That's why I don't consider
Chrono Trigger to be the "best game ever" even though I enjoyed the story a great deal. It's simply a rollercoaster with a predetermined start and end point.
I should have been more clear, I was mostly talking about western rpg's which I was more familiar with (when I was growing up we didn't have much access to jrpg's in my country). Almost all rpg's I can remember of from my childhood (goldbox style rpgs, ultima series, games like eye of the beholder which is mostly based on tabletop d&d 2nd edition which allows not only character customization but also party creation, then later games like fallout and arcanum) tried to give you many choices as possible in terms of character (stat/ability) building. Now that I learn (a little) more about jrpg's, I see the term can be interpreted very differently, it's nice and interesting.
And in the games where you can make decisions, sometimes one option is much better than another (who would spend any points on Dexterity in Planescape Torment?). So the question to answer in this thread is, what RPG is the best at offering meaningful decisions in character progression
Perhaps it is. I don't know. Meaningful decisions you are talking about is also very different for me I guess. An ability/cohice which is highly unbalanced but entertaining in terms of how it makes you feel -the amount of control you think you have as a result- (as in Armageddon spell in Ultima VII, which kills every living soul basically), is a much more meaningful and fun choice for me, compared to seemingly different but balanced powers that only pushes me through the same direction in story. In that kind of balanced game, sometimes I can feel like nothing changes except the effects on the screen -killing the same guys over and over again-, perhaps because I'm mostly playing for discovery and novelty value, not for tactical curiosity.
And then there are games like Dishonored. Is it an rpg? I don't know (and I don't care), but it sure gives you a lot of wiggle room how you choose to upgrade your character. Balanced? Don't think so. But I can guess a lot of people probably tried & liked the stealth walkthrough which is not meaningful when you look at it in terms of balance. Compared to killing everything easily in your way, it is cumbersome and right out unnecessary.
That's my answer to the original question which is about games that allow player to upgrade the charater any way they want. That is probably not the desired answer for a lot of people, though.
P.S.: Probably Fallout would get my vote for the best one I played which included a lot of wacky choices and was pretty balanced at the same time.