LogFAQs > #969453324

Genuinely all of these have been a factor at some point.

If you take Samurott as an example, it's a big mix of things. Firstly, I like the design a lot and it had serviceable stats; design-wise it was about even with Serperior (a surprise because Snivy vs. Oshawott is an easy win for Snivy, design-wise, imo), but Serp had godawful stats so I opted for Samurott. Movepool helps too - finding out that Samurott gets Megahorn was also a factor in choosing him. But I also chose Samurott because there weren't a lot of other water options that I was particularly into, and I wasn't going to chose Emboar because I'd already decided on using Darmanitan.

So in that particular case the thinking covered, like, most of the options there. (Oshawott was even kind of a meme in pre-release! But I can't stay that really affected my thinking.)

The #1 thing though is probably a combination of stats and design of specifically the final form. The base form doesn't matter to me at all - you will have the base form for, like 2 hours before it evolves.