Choosing which cards to collect

[Yaron]

I started collecting Pokémon cards at the end of the '90s, mostly focusing on English ones, but also some Japanese ones (Gym Challenge boosters and some promo cards that came with other Japanese merchandise). Somewhere around 2000 I lost interest, and the only thing I have left from that time is the Japanese collection.
I recently got an itch to start collecting again, but I'm only really interested in stuff up to the e-Reader era. I'm not going to get anything close to complete with the limited amount of money I'm willing to put into this hobby, so I'm trying to come up with a way to prioritise cards for purchasing.
Do you have some kind of system for these things? How do you choose which promo cards to pursue, for example?

 

[Ruffimutt]

I collect any cards I find cosmetically pleasing, as well as promo cards or cards that are unique.

Examples from my collection:
Pikachu Libre
Kanto Ash Pikachu
Pichu Bros
Mewtwo Pokemon Rumble