Well what would it be? Give a reason for your choice.
I chose salamence and all its related mons. If i was to choose a new one to go alongside this line it would probably be metagross to collect both gen 3 pseudos. I think that would be cool and im not ruling it out.
Lets hear your answers
I do Eeveelutions and Skarmory. But if I was to do a different species, it’d probably be Steelix. I loved how aggressive it looked in the gen 2 games. Probably no other reason than it looks cool. Just like Skarmory I guess.
Psyduck. Because he’s silly and a complete joke of a Pokemon, and thus my favorite 
I have a binder going already, but I would love to one day have the premier graded collection of Psyduck. Long term goal to shoot for 
@ragingkraken love this, solid choices.
@camrok37 psyduck is my favourite funny mon i think its up there with pikachu amongst the hardest to species collect though
I already collect the eeveelutions and the Sprigatito line, but otherwise I’d probably go for Meowth and Persian, Skitty, or Mew and Pluse and Minun! I think that this boi right here is one of the reason’s I probably wouldnt be able to complete the collection:
I would love to species collect Psyduck (or Slowpoke). Unfortunately, a lot of the Japanese cards are unreasonably expensive. It seems to be a fan favourite.
I currently have a haphazard Raikou collection, and I’m considering whether I want to start a species collection of Dragonair, the Poli line or Nidoking
We need more Delta Species in our lives. One of the cooler concepts they ever came out with.
yes!! also very tempting…
I collect all varieties (languages, holo types, etc) of Shedinja because it’s my favorite. Including non-tcg cards and such.
I’m also currently working on a binder of all Japanese bug type cards in chronological order of release, because bug pokemon are #1.
I collect Piplup line (obviously lol), but I also collect English Tandemaus and Maushold, which funnily enough I don’t think I’ve ever shown here.
If I had to pick another species, it would probably be Dratini/Dragonair- it used to be my favorite Pokémon as a wee child, and I’ve always kept a nostalgic kind of love for them. I have a small collection of them from that time period, but I didn’t keep up with it. I don’t think I’d ever do 100% all prints ever for another species, as the Piplups are a huge commitment already (which I love), but who knows.
Species collections are by far my favorite though, and I can see myself starting mini collections for other species later on down the road if I’m not careful. 
I like Tyranitar. At least in the TCG, Tyranitar has a ton of great artworks. It’s a shame Garchomp doesn’t really. All the best Garchomp cards heavily feature Cynthia. In fact, hidden fates shiny vault Cynthia might be my favorite “Garchomp.”
Rayquaza has tons of great artworks throughout the years. It might actually be a toss up for me between Rayquaza and Tyranitar highest quantity of great TCG art.
working on it…
Then of course Eeveelutions. Umbreon has the most high quality artworks, so I’d have to rank them Umbreon > Flareon > Jolteon > Vaporeon > Espeon > Sylveon. I know it was really needed in the games for fairy type to come in and rebalance dragon and steel, but I never really liked it.
I currently collect Dialga, Froslass and Virizion. Species collecting has become one of the most enjoyable methods to collect for me and I keep finding more Pokémon I want to collect. I’d probably go hard into collecting Arcanine. Once I get my money up
Gastly and Dragonair are my favorite Pokemons, I always keep thinking about I should start a binder for each. That would be fun but haven’t tried it.
I’m strongly tempted to start a Kirlia collection, it’s just adorable. I love the Gardevoir line since childhood, and also it’s an interesting choice I hope.
I considered both Celebi and Espeon in the past, but they were a bit overwhelming at the time, and espeon especially becomes pricey really quickly for a side project unfortunately.
I species collect Wailords in all languages.
my next three favourite pokemon to collect would be Quagsire, Whiscash and Centiskorch. I have not made up my mind yet if I really want to start to seriously collect them but in the meanwhile I will hold on to any card of them that makes it into my collection
I collect the Hoppip line in English and Japanese, both TCG and non-TCG. I might branch out to other languages once English and Japanese are complete or close to complete.
I also side-collect Wooper/Quagsire and Chinchou/Lanturn. I’m thinking of doing either all unique arts or max rarity in English (+ any Japanese exclusive arts). Haven’t quite decided yet, as I’m mostly focusing on my primary goals for now.
I don’t collect any species currently although, I’d definitely choose Arceus and Dialga as my preferred.
I currently collect the Mareep evolution line and try to grab them in any language when I can find them in my budget, as well as Cyndaquil and Quilava (Im kinda meh on typhlosion). If I had to go for a new pokemon itd probably be the wooper evolution line or Vulpix line. Those japanese vulpix ponchos can be a bit much though.
One ive been slowly working on is manphy, im not really sure what the draw is there but i cant get enough. I really wish there were more ferrothorn cards though, i would love a side collection of him as well.
