I'm a fan of regional dexes that mostly consist of a majority of the new pokemon, i.e. Kanto, Hoenn and BW Unova. Because it showcases the new pokemon and makes you more likely to use them and get to know them better, Kanto benefited from this since it was the first and there was no previous pokemon. That's one of the reasons why gen 1 pokemon are so popular. But the Kanto dex was very imbalanced still, lots of poison types, reused typings.
I don't like regional dexes with new and a lot of old mixed in like Johto, Alola and especially Kalos because the old shows up a lot and the new is more sparse. DP dex didn't even have all the new Gen IV pokemon in it, which I think is more silly than the lack of fire types. But Platinum really improved the Sinnoh dex. B2W2 along with Platinum are the best at combining old pokemon and new pokemon.
Speaking of Kalos, I feel like one of the few who didn't like the Kalos dex, cause it was so expansive and full of pokemon from all generations. I like being limited to certain pokemon which is I like the Unova dex and adore the limited options in Colosseum and XD.
Here's how I would rank the regional dexes
BW Unova > Hoenn > B2W2 Unova > Platinum Sinnoh > Kanto > DP Sinnoh > Johto > Alola > Kalos
The only reason the Johto dex is above the Alola dex is because I like Johto pokemon more.