Which is better, OCS or direct commission?

The Army isn't very big on direct commissioning any more. Unless you are filling a specialty position like a Clinical Psychologist, the Army tends to shy away and limit the number of direct commissions. A Medical Service Corps job is an admin/logistical position, not a medical one. That means anyone who meets the bare prerequisites for it - usually just a Bachelor degree - can compete for it. Because the bar is so low, they get filled quickly, and since you are in the NG, they fill by slots, and there may be no slots to fill. Point is, the likelihood for you to direct Commission into a MEDO slot is very low, but your chances of OCS are very high. If you want the federally recognized OCS you'll need to transfer to the USAR first.

You may be thinking that your time as a Psychologist and your PhD would make you mor competitive for a MEDO position, but a MEDO isn't medical, any more than a PAD clerk is medical or a 68J Medical supply is medical. A MEDO is an Operations officer, in fact my last MEDO was a 15P Flight Operations before he commissioned as a MEDO. Best damn MEDO ever. In case you're reading this Luis Espinosa - you're the GOAT!

Anyway, if you don't want to do your day job in the Guard, I suggest OCS and taking whatever job you can get. Just don't expect it to be in AMEDD. If you want to be something AMEDD, leave the NG first and join the USAR before commissioning

You should consider what your pay would be like if your unit deploys vs your current salary.

Direct commission is going to limit in what you can do in the military and whatever you direct commission into, that is all the Army really cares that you do for them as that is what they hired you to do. OCS gives you many more options to play soldier and that sounds like from the question that would be a better fit for you. Keep in mind the strength the reserves gives the Army is many do the same job on the outside which makes them better in many aspects MOS-Q to the AD side that get a lot of busy work never doing their job. Most reservists suck at the admin side of their job compared to AD as we do it everyday and generally our schools are twice as long. Chances are you will struggle in your job if activated and your MOS is not mental health. You will do it once a month until activated and during your inactive periods, you will be busy with your primary civilian job. Can people do it, absolutely but you did not ask for advice to get all 'flowers and rainbows,' you likely want the complete picture.