There is probably an array of reasons why some people like the second gen more then they did the first one. Maybe it is because functions like the phone that lets you do rematches, the day and night aspect, apricrons which allow for new pokeballs, new types, new evolutions, and of course the only game that allows you to explore two regions. Everyone has a different opinion of what is the best and what they define as "best generation". I personally like 3rd Generation the best one reason is it is actually the only region were I like all the starters another reason is I like a lot of pokemon from the generation. For some others they may have liked 3rd for the debut of Contests and EV's which vastly contributed to competitive battling.