There has been quite a few threads over the years:
- redcap.org/page/Character_Generation
- https://forum.atlas-games.com/t/comments-on-the-mysteries-revised-edition/4585/1
- https://forum.atlas-games.com/t/recalibrating-ars-magica-02-some-virtues/7437/1
- https://forum.atlas-games.com/t/pearls-of-wisdom-your-one-tip-for-character-creation/8748/1
For down time advancement, from a pure XP point of view:
- Strong Faerie Blood gives you 15 more years before Aging kicks in, about 225 xp
- Skilled Parens is 90 xp
- Puissant Magic Theory will save you 85 xp if you reach a score of 7+2
- Affinity with (Art) will save you 70 xp if you reach a score of 20 (after 10 seasons of reading)
- Book Learner will save you 60 xp if you read for 20 seasons, and that's easy to reach
For adventure time:
- some Magical Focus is best
- Flawless Magic, Flexible Formulaic Magic or Life-Linked Spontaneous Magic
- Cyclic Magic, Life Boost, Self-Confident
As for the Flaws, it all comes down to what kind of story you want to tell, what problem to overcome. A magus can wipe armies before breakfast, the challenge has to be elsewhere.