The Ditch Witch Sk850 with narrow tracks paired with bmg and stumper 220 is hands down the best rig for minis. The reasons for are almost endless and the single drawback (controls are second best to Vermeer) is trivial. I chuckle at other comparable rigs (e.g. minis with sideways grapples, minis with lower tip weights, minis that are over 36" wide, etc...) that I see trying to get similar work done. The Avant 420 is also incredible from what I've heard, but completely different. I have the Sk650 and am pleased with its performance, when it isn't in the shop (I bought a high hour machine that set back my business development a whole year...).
The biggest issues are:
0.) Shop time - what's your backup plan? Do you have two minis? When my mini goes to the shop I get much more clever with my wood management than I otherwise would be...
1.) Who on your crew do you $30,000 trust not to tip it (surprisingly easy to do although I haven't yet...), or hit a fence? I can't be in the tree and also drive the mini. When the mini is behaving sketchy, I can't put a groundie on it.
2.) Recent issue - The hydraulic motors on my unit are designed for rotary attachments (trencher, stump grinder, etc.) and get dead-headed when using the bmg, which is a binary/on off type of attachment. My mechanic is looking into this issue as my bmg starts to slowly release wood that's been grappled. If anyone knows about this, pm me so that we don't hijack the thread.
3.) Imho, there is a narrow effective zone for a mini, that exists between the Stein arbor trolley + groundies, and a full size skid. A mini skid involves the costs of the mini (repairs, rigging time, track damage prevention/repair, maintenance), how much weight the arbor trolley handles, and the limited diameter that the bmg picks up (which tilts the balance towards both the full-sized skid and the arbor trolley). If I had to do things over, I'd grab an arbor trolley first because being dependent on a single machine burnt me.
But when the mini runs, it gets *work* done...