Well, from a mining equipment standpoint, here are my personal opinions on specific engines used in one particualr mine, in no particular order:
-All of the older equipment ran air cooled Deutz, from 4 cylinr up to v12s. I have to say they are one tough engine, and will take a lot of abuse. BUT... they fall short in local support and parts pricing, very expensive to repair.
-Cat 3406 (Ithink), very reliable, dont remember ever having to get support or replace anything on the engine. Downfall to these particular engine for underground use was emmissions, but then again, we are talking older generation engines.
-Detroit 50 series- Quite reliable, inexpensive to repair, excellent support, but I do remember some problems with them. I wouldnt call them bulletproof, although they were pretty good overall.
-Deutz liquid cooled B4fl series- engine itself seemed ok, but had ECM issues, no local support, parts or labor- would not use if I could avoid it.
-Cummins QSB series-(note that they are all 2005 and later engines)- very reliable, I do not recall any issues that were not self inflicted by the miners (hydraulic oil in the fuel tank). Local support is great for service and parts. I would not hesitate to use Cummins.
I worked for NY state for a short while, all of their large truck engines were Cummins until recently when they started buying Mack Trucks. The Cummins engine were pretty trouble free there also. I dont have much good to say about Mack in general, but I had not seen any major problems with them either unless you count the 3 year old engine with a rust hole through the engine block.
keep in mind, this is personal observation, from my own experience. My opinion to answer your question, would be Cummins.
