Some types were very easy to pick (i.e. Normal, Poison, Ghost, Psychic, etc.) and were obvious choices for me, others were a bit harder to choose and I changed them a couple of times (especially Water, Fighting, Ground, Bug, and Dark).
PS: I have the second largest Pikachu collection in the world btw. Tom, an online friend and fellow Pikachu collector from Belgium, has a few more than me.
Mines heavy on the gen 1 those nostalgia feels are too strong! Some tough choices there, Alakazam and Mewtwo is almost a toss up for me! Also tough decisions in the bug category with Caterpie, Beedrill and Scyther all close, but Butterfree pips it!