This is an age old question. There is not a clear consensus on this. The majority swears by sponsors, but a good percentage of devs find that they do better with ads. My advice would be to try putting a little (like 200 to 600 robux) into both just to see what happens.
Advertisements do work, you just need a seriously interesting ad for the best effects. I’ve seen it work before and that’s how a lot of false advertising works on the platform. Even games with terrible scripts/modeling/whatever you want to consider even get players. I don’t see how advertising doesn’t work because there is problems on the current platform caused by UGC ads.
It’s strange because when I sponsor and advertise for the same amount the advertisement gets more clicks yet the sponsor got me a stream of players for the next week or so, overall the sponsor was a lot better for me.