I won’t say Raichu as I’m nearly up to date with them.
I feel like I’d do pigeot. I am sure I took pigeot with me on my first pokemon adventure back in red.
Potentially corviknight. I’m in the UK and I caught a shiny rookidee (first form?) within an hour of starting Sword and Shield. That was when I started playing the games again with my partner that led me back to card collecting. It’s a great UK translation from blue tits and ravens
I’m not a species collector but I think Magneton would be fun. Numerous vintage holos, lots of variants, some difficult gem mints, some semi-unattainable stuff, very few bad illustrations and comparatively affordable.
Currently collect Umbreon, Espeon, and Torchic.
Thinking about other species makes me tired 
pretty much any of my 6 pokemon listed
Rock/Ground/Steel/Poison/Dragon are my thing
I’m already collecting Pikachu and Seviper, and I’ve collected Mimikyu in the past. So that’s enough for me… But if I would start a new one 
, probably one of these: Alakazam; Haunter; Sudowoodo; Torterra; Joltik; Archeops; or Cresselia.
Greetz,
Quuador
Mareep line is also 
One day I’ll start on the Squirtle collection, too many goals to complete before then though
That is a very diverse and unrelated list of Pokémon lol
Half my faves were easy: Wishiwashi, Surskit, Dondozo… they hardly have any cards yet.
the other half is pain: Gyarados collecting; Wailmers, probably going to try Kingdra…
If I wasnt collecting Eevee, Id probably pick Mawile, Klefki, or Kubfu. I like cute pokemon.
I’ve often considered species collecting Nidoking or Volcarono.
To drop in a rather special one: Haunter. Haunter has a special place in my heart and places in my list of favourite pokemon. He has great card artworks and his cards are affordable
I collect japanese porygon cards. I would most likely also collect Vaporeon cards.
Bulbasaur #001
I collect eeveelutions and kabutops for myself, vulpix for my daughter.
If i was to branch out into another one ir would be dragonair or gengar
While my main focus is my Eevee species collection (EN/JP) I’ve also casually picked up a few Calyrex cards over the past year.
But if I were to seriously start a new species collection, I’d probably go with Pokemon who were on my original Diamond/Pearl team, like Burmy/Mothim, Shinx/Luxio/Luxray, or Chatot.
I have my Togepi line & Jirachi species collection and that’s my main focus in the hobby.
I had English art sets of Lucario line, Piplup line, Shuckle, Sudowoodo & Lapras at one point, but sold or graded much of that to fund the expansion of Togepi line & Jirachi to English (and hopefully one day Japanese) master set
If anything I would just expand those further to other languages too.
But if money wasn’t an issue, I always loved the idea of adding Mew & Celebi species collections alongside Jirachi and the Togepi line.
…Oh and I’ll probably start a Gholdengo collection this year.
Porygon, Ninetales, Venomoth, Parasect, Sandslash Lines, except im too broke to be buying cards. (These are my fav mons and i alr have small collections of them. Cheers!)
Apart from the Marill evolution line, I’d say
Mantine
Dedenne
Raichu
I love the old back Dragonite cards too!
