Heart Gold and Soul Silver a good remastersecond of my personal favorite generation. Both X/Y and Omega Ruby and Alpha Sapphire added cool features. Unfortunately, the coolest features of each are EXCLUSIVE to each >_>. I personally recommend X/Y myself, I really enjoyed it.

I can understand disliking ORAS since they were extremely lazy remakes, but I just love the Hoenn region, so that's why I still enjoy ORAS.  Emerald is my favorite Pokemon game and probaby always will be.  To me, XY felt like they had so much potential, but there were many issues for me.  I was really hoping that a Z would happen to fix all the issues, since the Kalos region is pretty beautiful.  To me Diamond and Pearl were pretty terrible games as well, but Platinum fixed almost all the big issues that were there and that game was great, so I was hoping Z would do the same.  XY just feels like unused potential to me which is the biggest reason I dislike it, also almost every character was just awful, especially Tierno and Trevor.

I'd suggest just waiting for Sun/Moon if you don't mind a few months. If you need some Pokemon right now, maybe Black/White. Good games, will introduce you to some of the new Pokemon, and you'll definitely appreciate the QOL improvements in the 3DS games when you get to them.

Heart Gold and Soul Silver or Black and White. Yes they are DS games but they are the best available on 3DS

I'll have to go against the grain here and recommend X & Y over OR & AS. I never really took to Gen 3 (Ruby/Sapphire) when I first played it, and even with the extra polish of a remake, I still find the Hoenn region to be one of the most boring in the series. Meanwhile, X & Y has actually become one of my favorites, behind Gen 2 (Gold/Silver),

You could always just wait for when Sun & Moon release, or buy one of the Virtual Console options (Red, Blue, Yellow) which despite their age are still pretty enjoyable imo

If you are talking this gen, my favorite is Omega Ruby and Alpha Sapphire. I absolutely love those games. X/Y are pretty good too but honestly I think you should get Black or White as well as Black 2 or White 2. Those are the best in terms of story (especially B2/W2)

Silver is the best one I have played

I'm playing the original Ruby now emulated on my psp because of this pokemon fever too xD I never played it before but I'm enjoying it quite a bit.

Silver is better though.

From a value point of view, the gen 6 games are still being sold at $40, the same price of Sun/Moon, yet Sun/Moon will have more content and better production values.

Also, online for DS games is dead and most of the playerbase are on the newest games, so I advise against getting a gen 5 or lower game, unless Pokemon's singleplayer alone can actually satisfy you.

Hard to say, playing the originals on VC will probably not do you much unless you're really into playing the originals. If it doesn't give you a nostalgic feel, then it could be hard to recommend it because the series HAS evolved over time. I know, hard to believe since fans have been crying that the games haven't changed >.>. The gameplay for the originals are notably different from the more recent games, there can be a sense of imbalance (those damn Psychic-type Pokemon...) and there is more commitment to grinding (not sure if you're into that). But I wouldn't be mad if you ultimately want to play these games. Despite their flaws, the original R/B/Y are among my favorite games of all time and experiencing them at least once is good to see how much the series has grown.

I'd say go with gen 4, 5 or 6 due to their ease of accessibility (though prices for gens 4 and 5 may vary). You'll probably find something to your liking going with any of these options.

Play 5th gen for the story, it's significantly different between B/W and B2/W2 so if you don't want to buy one of each pair buy B/W and later on purchase B2 or W2 (the story of B2/W2 takes place 2 years after B/W so you'd be missing on quite a lot of plot), keep in mind that many people prefer the story of B2/W2, also X/Y, the upcomin Sun/Moon and Super Mystery Dungeon !