As a armed professional, I'd highly suggest a well made level II rentention system. A holster like a SERPA, Blade-Tech Thumb Drive, SFS/ALS, etc. You are more likely to encounter a subject or subject who may try a weapon snatch. You might also need to run, jump, roll around, climb, etc. I've had a few sidearms slide out or drop & it's not good.
A secure, strong-side holster is a lot better.
Now if you want speed or carry as a armed citizen, a open top style may work better. As noted instructor & sworn LE officer; Massad Ayoob says, you should always use a well made holster that you can quickly access with either hand & reholster one-handed with ease.
Some concealment brands have a band around the top to aid the re-holstering.
Whatever type you choose, check it often to make sure it's clean and works correctly. You want your sidearm to be there when it's needed.