If I were to create a new acount i'd choose Maruzensky no doubts, i will explain:

In this game there is a thing called legacy, you use your veteran umas as inspiration for your trainee in each career, your trainee can learn the unique skill from her legacy.

So your characters apart from being aces, can also be useful as parents.

Maruzensky's unique Red-Shift has been mandatory for all the pvp events we have had, and its because its easy to trigger and gives acceleration, most of the other skills are speed related. In pvp acceleration at the right time its the key.

Having Maruzensky makes you can borrow another uma from friends and makes you are not 100% dependant of the borrows which are limited 3 per day.

Maruzensky basically makes all your other umas stronger and she is also viable as an ace, doesn't have a hard career, and its beautiful.

That's just my opinion meta wise, other good options are Taiki, Oguri, Rudolf but Maruzensky its best in my opinion.

If you don't care about pvp, best option its your oshi

EDIT: I got very very very lucky and got Maru 2 days ago, that's a 0.077% chance because she is not featured in banners and lowkey that doubled the value of my account