Well, I never dated but in theory I was definitely a "Nice Guy", and most my friends were too. I sort of cherish the experience because of the peer group that put me in, even if I personally turned out not to be a "nice guy" but rather a "nice girl", for the reason that now I know for a fact those nice guys exist and that is my type.

I know the pitfalls of pretenders, the red flags to look for, the signs someone is a nice guy but too shy to say anything, etc. It's a common complaint by guys when they start to get bitter about it (understandably I feel) that many women say they want a nice guy but then always go for the jerk. But I believe that isn't because of any sort of hypocrisy, but rather simply not often having had the chance to learn the dynamics of the nice guy vs the jerk who just pretends to be nice from behind enemy lines so to speak, and that most women who wind up in jerks while saying they want the nice guy are just being genuinely misled.
Also, important point to make. There are 100% nice girls who a lot of guys don't give the time of day. It's not a purely guy thing just because that is the cliche.