You can only do one, which is better for your game?

Weekly lessons.

Nothing beats hitting balls while a coach supervises. Your focus is on good swings, control, contact, tempo. You let someone else's eyes watch where the ball goes. This repetitive practice gets you where you want to be faster. Why do you think the pros have swing gurus?

Playing 9 holes 3 days per week for sure. Lessons are great, but it's still only range time ... and hitting a bucket at the range is fun, and can be productive, but you'll get way more out of playing 9 actual holes 3 days per week. It's also the only scenario where you'll be putting ... which is, as we all know by practising, the best way to lower your scores and becoming a better golfer.

depends on how good of a golfer you are....if your a beginner take lessons for a couple of months then go play 9 holes 3 days a week....if your golf swing sucks it will never get better playing its all about muscle memory

Taking lessons once a week because golf is one of those sports where anyone can practice all they want but you need to practice properly. If you practice w/o lessons, you begin to develop bad habits and then you set those habits in stone by practicing without being taught. That's my opinion.