Zapdos: Hidden Fates 44/68 (although I also like the Pokémon Rumble Zapdos with its little beak 
)
Moltres: WotC #21 promo / Japanese Pokémon Web 043/048 (big surprise there, haha)
Dratini: Dragon Majesty 34/70 (haven’t seen this artwork before, but it looks amazing - EX Delta Species 66/113 is a close second)
Dragonair: Base Set 18/102, although Dragonair has a few more amazing artworks
Dragonite: Legends Awakened 2/146
Mewtwo: Shining Legends 78/73 (without Mewtube this would have been so hard to choose… some other amazing ones: WotC #12 promo; BW-P Battle Carnival Jumbo promo; Mewtwo & Mew GX tag team SM191 promo; etc.)
Mew: Hidden Fates 32/68 (another pretty difficult to choose one, but there is just something about this cute Mew I really like - some other amazing ones: Japanese CoroCoro Shining Mew; Japanese 033/P McDonald’s promo; Mewtwo & Mew GX tag team SM191 promo again; Ancient Mew; etc.)
Chikorita: Expedition Base Set 100/165 (with the Generations - Radiant Collection RC1/RC32 as close second)
Bayleef: Lost Thunder 7/214
Meganium: Neo Genesis 11/111
Cyndaquil: Neo Genesis 57/111
Quilava: Neo Genesis 46/111 (most of Quilava’s artwork are a bit lackluster imo, even though I do like the design of the Pokémon itself quite a lot)
Typhlosion: SM185 promo
Totodile: EX Unseen Forces 78/115 (Totodile is such a happy Pokémon, so it also has a lot of nice artworks: Neo Genesis 81/111; Expedition Base Set 134/165; HeartGold & SoulSilver 86/123; Phantom Forces 15/119; Japanese Movie Commemoration Random Pack 006/022; etc.)
Croconaw: 009/T promo (another artwork I hadn’t seen before, but which looks amazing)
Feraligatr: Expedition Base Set 12/165
Sentret: POP Series 7 16/17
Furret: Neo Genesis 35/111 (although I also like the Aquapolis 48/147 and HeartGold & SoulSilver 21/123 artworks, I’ve always liked the Neo Genesis artwork, and it also gives me a nostalgic feeling. I remember I lost my Neo Genesis Futtet as a kid, so when I came back collecting five years ago, the Furret as well as the Legendary Collections reverse foil Moltres which I once traded away as a kid, were one of the first cards I bought. 
Oh btw, @pokemontrader . You’ve created a dilemma for me, haha. I actually want to start saving money a bit again after I’ve made a lot of expensive purchases, but thanks to your series I kinda want to replace all cards in my national index collection with my favorite artworks one day, rofl… 
Greetz,
Quuador