First off, I am an automotive technician at a Jeep dealership (previous to that, a Dodge dealership, and independant shops).
To discount a make because "I hear they have bad transmissions", isn't exactly fair. If you were to disregard a model, because of a common problem such as that, you'd never buy a new car. They all have their problems, they all have their upsides. It's really a matter of personal preference.
That being said... Just have your father spend an afternoon and test drive the different makes. Then find a better way to buy one, then through some greaseball salesman at the local dealer. If you are trading something in, and must go that route, find the "fleet" salesperson. They aren't as interested in hardballing, like the typical greaseballs. (Can you tell that I
hate car salesmen.
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Grand Cherokees will only seat four comfortably, and five in a pinch. The Durango's are good, but make sure that he likes the size. (Yes they are a mid-size, based on the Dakota.) And with the V8 engine, the Durangos haul ass.