Any particular year of Crosstrek better than the other?  Trying to help my brother pick a used one and not sure what year to look at.

dunno really, read that the early ones have a reputation for being underpowered. Maybe check cars101.com for features?

I was thinking more along the mechanical lines....

2017+ for forester, I’m not versed on crossteks specifics but I’d lean that way too for crossteks too. 
 

Issues to research and somewhat avoided by later models:

CVT

oil consumption

Crosstek valve springs 

'17 in my shop right now with a rod knock. 69k miles. 

Just did a '16 Forester that had a broken valve spring at 120k. Nothing else wrong just a broken intake valve spring. 

GD

Valve spring, interesting.