It really depends on how you define "better". If the definition is to be taken as "which game was most enjoyable", then there is no correct answer. There is only the correct answer for you.
Nostalgia is a very good thing. In fact, its a sign that you are hooked on a game, tv series, etc and that's what Pokemon is supposed to do.
Another definition could be which game(s) were more "popular". This is where people tend to get into arguments, because they all struggle to identify the exact definition and successfully convey it to the other party. There are many more factors in terms of sales & marketing, economic conditions, etc than people realize. All of which affect the size and scope of each generation's fanbase, and all of which contribute to the growth/decline of the franchise.
I'm a strong believer that the best contributor to growth is through social influence, which affects corporate decisions. When positive word of mouth is strong and the fanbase is lively, the franchise is most likely to prosper. Likewise the reverse is true and the brand will suffer under negative actions. A perfect example of this is both the relentless opposition and venemous reactions to "genwunners", which has become more an opposition to "nostalgic fans". Odds are the more divided the fanbase is, the worse off Pokemon actually is because it causes declining growth
I support Save Our Voice Actors, a Pokemon fan group in favor of returning the voice actors in the anime dubbed by 4Kids (seasons 1-8). facebook.com/saveourvoiceactors