Hi, when buying a new macbook what is it advisable to do? Do a fresh install or use time machine?
If you use TM do you transfer junk that has accumulated over the years? What is best performance-wise?
Depends how much stuff you've got on your TM backup and how easy it would be to reinstall. I'd always say a fresh OS and reinstall from there, but that's just personal preference and more to err on the side of caution. If that'll involve too much effort, just restore from TM backup.
It's really only a question that you can properly answer.
I don't have a lot of stuff and all files are in dropbox, so easy to migrate. I would save time installing Office and Adobe Creative Cloud essentially (don't have much more). Not sure whether TM would save account info and preferences.
BTW, I got Windows 10 for free as I was betatester. In theory it should work only on the original machine, do you think that it will work if I migrate from Early 2015 MBP to the new one? I think it has to be with motherboard.
I personally hate migrating data automatically. I just have to know that I'm running on a clean system.
When I was less lazy I always fresh installed every major OS release as well instead of updating.
Be aware that you are -not- migrating old system files, only apps, accounts, user data, and settings.
BTW, I've read reports that the migration actually gets done more quickly if you first clone your old Mac to an external drive (using either CarbonCopyCloner or SuperDuper), and then let Migration Assistant "work from the clone"...