My two favorite artists are Naoyo Kimura and Mizue.
Naoyo Kimura has been around since the beginning, and he is well-known for his Tropical Island artworks, as well as a bunch of amazing artworks during the Neo era. He’s also still active nowadays, with for example his Light Toxtricity artwork (shown below) for the 25th anniversary.
Mizue has been around since the start of the Black & White era. She likes to use effects for bubbles; sparkles; sunlight; wind movement; etc. in her artworks, and a lot of them are also very cute.
Here six examples from both of them, of which the Moltres from Naoyo Kimura is my favorite Pokémon TCG artwork and the Swablu from Mizue my second favorite, both of which I have a small collection dedicated to: Moltres, Swablu.
Seeing the artworks of both under one another, I like that Naoyo Kimura uses a lot of darker backgrounds and Mizue a lot of lighter backgrounds. (Probably a coincidence with the six I picked, since Naoyo Kimura has also done a lot of lighter artworks, like the Southern Island I mentioned earlier.) 
Both of them are amazing in their own rights, and I love (almost) all of their artworks.
Greetz,
Quuador