It's a no brainer.
Oligarchy and Landed Elite are pretty inconsequential, even if you have 15 cities. Legalism can be gamed to deliver big hammers by adopting it late in the game, particularly for a cultural victory or as Siam for earlier Wats. Oligarchy is useful for building wonders. The tradition opener (+3 culture in the capital only), Monarchy, and the tradition finisher (+15% growth in the capital) are all good boons.
So, if I want to build wonders, I'll adopt Aristocracy. If I know my capital will be a substantial portion of my empire's output, I might go all the way to Monarchy. But I'd probably only finish the tree in a cultural victory.
The no brainer part is that Tradition is not a very desirable destination overall. But if you only have 2 or 3 cities, the Liberty bonuses to your empire are even less desirable.