Depends on what u use the bike for…….
I ran 1 x 9 for 4 years, changed to 1 x 10 when I built my latest steed (Cotic Solaris)
I use my bike mainly for trail centre duties and it is perfect, nice spread of gears.
Running 34T chainring with 11-36 cassette.
Bare in mind u will need some sort of chain device.
I have a Pauls chain keeper: