I prefer metal minis just because I like the heft of them. Plus they don't get blown around as easily. But as several others have mentioned, for the ash and trash of an army, or a large encounter it just isn't worth painting dozens of generic monsters. For low level encouters with the gaming group or for use at cons the prepainted are the way to go. If one comes up missing or is destroyed no biggie. If a personalized mini comes up missing that is a different story. For a unique monster, a prominent NPC or for a PC mini you just cannot beat a well painted personal mini though.

I have a fairly extensive collection of metal minis that I have gathered over the last 25 plus years. I have only painted a very few of them, mainly because of too many things demanding my time. My painting ability is good enough for gaming although I will not win any contests with them. Maybe someday I will be to that level but I have never been dedicated enough to get there. What can I say I am a slacker.

So it boils down to: A) I like and prefer metal minis, B) I use a lot of prepainted minis (refer back to being a slacker), and C) someday I will use more metal again.
Democracy is two wolves and a rabbit voting on what is for lunch.

Liberty is a well armed rabbit contesting the vote!