Should I focus on Aukštaičiai or Žemaičiai pronunciation?

I'm an absolute beginner who keeps bouncing between apps, and I've noticed my audio materials use different regional accents. One sounds much flatter while the other has distinct vowel lengths that are really confusing. Which dialect is the standard for a learner living in Vilnius, and does it really matter for my first six months of study? I am asking specifically about learning Lithuanian, not a generic study routine.