Start with the mobile mechanic unless the failure is obviously internal (engine knock, transmission grenade) or the truck is unsafe where it sits. Most breakdowns are road-fixable, a service call costs a fraction of a heavy tow, and even when the verdict is "this needs a shop," the on-site diagnosis tells you exactly where to tow it and why — so the tow you pay for is the right one.
Heavy towing is the most expensive way to move a broken truck, and a surprising share of tows carry trucks that could have been fixed where they sat. The economics favor diagnosis first in almost every ambiguous case: air problems, no-starts, electrical, tires, cooling, brakes and most derates resolve roadside, and the service call plus repair typically lands well under what a heavy wrecker charges for the hook alone.
The exceptions where towing first is right: unmistakable internal failure (a rod knocking, gears in the oil pan), a truck in a genuinely dangerous position, or damage that makes it unroadworthy regardless of repair (wreck damage, seized wheel end). Safety position beats economics every time — if the truck is in a bad spot, move it first.
When you chat with RIG dispatch, this triage is the first thing that happens: symptoms, photos, and location tell the network whether to bid a repair, and if the honest answer is a shop, dispatch helps arrange the tow to the right shop rather than the nearest one. One description, either way.