Is idler drive better than belt drive or direct drive?

The most succinct answer to your question is: Rock, paper, scissors.

LOL. MC.. Crack me up...I'll take ROCK...

 I like direct drive, when it's party time...YUP. 

I like rim, idler with belt, and belt drive when I'm getting serious with the ol vinyl.. Not as often as it should be...RUSSCO.. Garrard KILLERS
Check them out. LOL they have a gear shift.. I love them..

I like hand made too.. fun to mess with..

I own them ALL, 401 (better unit) 301 better looking, TD124s, are a work of art... Russco/Sparta/GRK. 750 Fairchild (my personal favorite) got stolen.
24/7/365, for 30 years, then 200.00 USD worth of parts, another 30.

Regards

Here we go again. I do not know where this illusion that an idler wheel turntable has more "impact" and "drive." Music has impact and drive. Turntables do not. They just spin, hopefully at a constant and noiseless 331/3 RPM. Idler wheel drives are relatively a mechanical nightmare. They were necessary 1/2 a century ago to shift speeds and give a turntable enough torque so that a record could be slip Q -ed. Direct drive tables replaced them and radio stations never looked back. All these idler wheel tables out there were dirt cheap and great for cottage companies to mess around with the resurgence of vinyl. 
Even if an idler wheel table was quiet to begin with, with just a little wear  it won't be. Anybody with an excellent sub woofer system that operates flat to 18 Hz can not use one without turning on a rumble filter. As an idler wheel drive wears you get rumble, wow and flutter. As a belt drive wears you get just wow and flutter. Direct drive tables do not wear and they are the most accurate speed wise with just a few exceptions.
The only reason I would ever buy a vintage table is for a conversation piece. Impact and drive? Only by the power of suggestion.

There is no good or conclusive answer to this one as it all depends on system synergy and your personal preferences and obviously the tonearm, cartridge, phonostage, amp, speakers attached to it....lol.

Just too many variables to state anything conclusively.

As Mijo knows I am a big idler drive proponent owning a top flight refurbished Garrard 401 with a Micro Seiki MA505LS arm with various mc carts, Dynavector Karat ruby, Koetsu Black Goldline, Ortofon Cadenza Black etc.

Now I have recently acquired an Avid Diva 11 SP Belt drive TT that I am putting through its paces right now as a worthy challenger.

So far results are impressive but I would say it just does not have the low down drive and propulsion that the 401 does.
Now call that evidence of rumble if you will, I truly dont care as its in my system and my old ears like the sq and at the end of the day that is all you can say about it.

What I would most likely agree with here on Mijo post is that if you have an old idler drive that has worn parts then it is likely to sound worse faster than a worn belt drive table but there are MANY "cottage industry" suppliers to bring Garrard, Thorens, Dual etc more than back to life and vastly exceed original performance.

Yer pays yer money and takes yer chances!

They can all be good depending on the execution of the designer.  A well reconditioned idler at a modest price sounds wonderful to these ears.