>>38751805Gen 3 is best played either as the remakes or emerald thats in some areas even better.
Platinum is suggested and gen 4 in general shouldn't be skipped because it introduces the phys/spe split making some mons better, some worse.
Hg/ss are the ones to go for the johto experience but note that they have not fixed the somewhat horrendous lvl-curve.
Bw and bw2 are both worth playing but take a break by playing a spin-off by the name of pokemon conquest so you dont risk being burnt out for playing through the same region with somewhat big changes twice. Gen 5 is on the more mature side and often appeals more to teenagers and older fans with its humor and style. (Image related)
Gen 6 is a mixed bag. I myself enjoy it a lot because I rotate my party and fill the pokedex thus not suffering the exp shares tendency to overlevel your party. The online features are the best in the series.
Gen 7 is challenging while that may not seem to be the case. Usum has a bit more cutscenes but it fixes a lot of content. It has the problem of having a slow start but the games are fun if you are interested in a tropical region and do not mind moving on rails for about half of the game.