Best fitting rear heel pieces? Grivel if your boots are big enough
best fitting front bails? Petzl..will work on all three brands
BD isn't terrible on either and I really like their heel levers on any boot or crampon.
Both are easy to do. Done it many times with Petzl front and rears or better yet Petzl bail and BD heel. Narrow welts on the 2.0 but nothing like the Scarpa Ultra for example.
Why not just purchase and use the crampons that are DESIGNED specifically for LS's?
If one does their research, they will indeed find out that Grivel and La Sportiva work together on design aspects had have done so for several decades.
Mix matching components makes absolutely zero sense.
I am calling bullshit on your Petzl bail claim. We dumped Petzl's cus their front bails have popped off on several type boots that many of our clients use. Grivels are far easier to "slip" into and have consitently stayed on, securely, without any failure for the past six or so years, on all boots that them clients utilize.
The rotation of the RING that attaches the front plastic/rubber component on the P's can get compromised either by grit or water that freeze at the attachment point. Grivels pin attachment alliviates that problem. Makes a world of difference when one is trying to attach their pons on a cold morning at altitude. Frustrating to say the least. The Griver plastic component covers well over 25% more of the toe btw.
As far as the metal front bail system for either, I just measured them both and Grivels surround and fit the the toe of the LS boots far more tighter/snugger.
From my experience, Scarpa and Petzl are a match as are LS and Grivel with the metal front bail systems. But! The new G20 front bails fit like a glove on both Phantoms and any LS boot (Batura's).
BD pons have the same retainer pin system as the Grivels. I/we do not prefer to utilize them in our rental inventory nor personal use.