They're called scoring clubs for a reason.
Ping Rapture 12.5
TEE CB4 Tour 16.5
Ping G 19/22
Ping i E1 5-U
Ping Glide ES 54.5/60
Ping iN Half Wack-e
I think it's different for different handicap levels.
At one point I would have said the putter but someone on here not too long ago claimed the irons (specifically the shorter ones, say 7-PW) were the most important clubs and I think I've come around to this way of thinking.
If your driver's horrible, you're not going to have a good/great round but if it's "just OK" you still can.
If your putter's horrible you're not going to have a good/great round either but if it's "just OK", you still can.
But if your irons are horrible you're going to have a poor day. If your proximity to the hole is poor but you're still hitting greens with your irons you'll still have a good day.
The truly great (for ME of course) rounds I've had were ones where I was hitting greens, and close,,,,,,,,,, and if you're hitting greens you're going to score. If you're hitting greens with your irons there's little chipping needed. If your hitting greens with your irons it takes the pressure off your putter.
And of course the the closer I got the irons to the hole, the better the round. Hit enough of them close enough and you'll not 3 putt at all and you probably will make a few.
I think it is the driver, because it gets the game started. So is it drive, arrive, or putt?
I understand where others are coming from with saying driver/drive is their most important as well as putting. Starting off in a good position and capitalizing it with minimal strokes on the green are essential. For me personally, it may also depend on the course. Wide open links I'm going with irons/wedges 9/10. If I'm mishitting my driver I'd aim to compensate. But that puts extra pressure on my irons/wedges to pick up the slack as I'm now probably anywhere between 30-60 yards off of where I needed to place it. Close approaches kind of negates below average putting. I don't necessarily need my putting to be my best aspect if I can stick it within 10-15 feet. Tight parkland course though I'm going with driver/drive 10/10. Scores skyrocket when I have to start playing punch shots under trees every hole. If I get it near my desired target off the tee, I can play my irons/wedges that I know my misses wouldn't be near as offline compared to a driver.
I think one also has to look at strokes gained from poor shots at each of the club levels OP designated. I am just beginning to explore strokes gained, so I don't quite understand it fully yet, but if a poor shot with one level of clubs consistently drops ones strokes gained compared to the other levels, then that should be your most important club level.