GB and GBC might as well be the same era for me, personally speaking, since Pokemon Launched a month apart from the GBC, and most people who I knew were playing pokemon didn't have an original brick size GB. That, and Pokemania was still in effect when gen 2 hit. It really hadn't lost momentum until the first teasings of gen 3. So I put those two eras on top for all time.
GBA was just okay. There was a clear drop off at this point, a lot of cut features like the day and night cycle, and trading back to prior generations, the first time pokemon ever felt like "one step forward two steps back", and the Kanto remakes were not so hot due to the bad soundchip and ugly colors. But the Gamecube games kind of bolstered this era a bit. I'd put this era in 3rd place.
DS era started weak with Diamond and Pearl but came back around with HGSS and Platinum and ended things with a bang with gen 5. After HGSS was so content heavy, Platinum saved the mediocre DaiPer, and Black/White actually put a little more effort into the writing for a change, it seemed like things were going to be alright. Only downside was Battle Revolution was ass. This era gets 2nd place.
And dead last for me is the 3DS era. It started okay with X and Y, but aside from the fact that it was 3D and had a huge dex and the Megas were kind of cool, it was a pretty underwhelming follow up to the DS era. Even the remake seemed like a step back in quality, there was no Pokemon Z, Pokemon Sun/Moon was too boring to finish. I didn't buy Ultra Sun/Moon because I couldn't even tell what was different from the trailers. And Masuda is too retarded to understand that there's more appeal to Stadium style games than just being in 3D, so he thinks we don't need those kinds of games anymore.
Can't really rank the Switch Era. All I played was LegPee and I couldn't finish it. Looks like end of the road for me and pokemon unless I start hearing some really impressive shit about gen 9.