Old mapler here who just got back into the game. In normal MS, PQ from level 35-70 was good because of Ludi's EXP rate and Orbis glitch PQ, but in the high rate private servers I've tried, it's crap because training gives much better EXP all the time. Since this is a low rate server and I see quite a number of people doing LudiPQ, Are PQs effective for EXP or am I better off training on monsters instead?
I haven't really tried either Orbis PQ nor Pirate PQ (which are the two most common PQ's for level 51-70 or so) but from what I've heard, is that it's equivalent to that of leeching. Meaning that the EXP is really good - much better than training itself. In regards to other PQs like Kerning PQ, Ludi PQ, I'd say the EXP gain is on par if not a little bit better than training. So all in all, I'd recommend a mixture of the two since the EXP is relatively the same, with the exception that as you get higher in level you'll get stronger so grinding might be a bit better.
On top being good exp wise, PQs also help you meet people who are around your level and that you can grind with in the future! I know I found a lot of friends when I first pqed ^^