My favorite in order. (This is entirely my opinion) Imma list the problems in each gen and positives.

Gen 1: Bad: Full of glitches and extremely broken. Good: At least it was a good challenge.

Gen 6: Bad: WAY too easy that its a joke. Good: Mega evolution was pretty cool.

Gen 2: Bad: Has some pretty forgettable characters and recycled some thing out of gen 1. Good: Had some challenging battles like Red.

Gen 4: Bad: Was too slow and not alot of original pokemon. Good: Was actually harder than most of the main series pokemon games.

Gen 7: Bad: Slow, too much Japan only events, and pokemon are too slow. Good: Had cool pokemon designs and z-moves.

Gen 3: Bad: Water, the encounter rate was high, can't complete the pokedex (no mythical pokemon aren't needed to complete the pokedex) due to Ho-oh and Lugia being event exclusive unless you had some way to transfer them from gen 2. Good: Fun and challenging, the battle frontier, wireless communication was introduced, and legendaries were hard to get to and find.

Gen 5: Bad: So many bad designs for pokemon and karablast and shelment by itself. Good: The hardest and most fun games in the series, story was just right and didn't invade the game too much or too little, and so many pokemon to choose from.