I would say the most important thing is how it's been maintained. I would rather a 300 hour engine that's been regularly used and properly serviced to a 50 hour one that sits for a month or two between uses and maybe had a service missed. Even what we could call a high hours engine is nothing compared to what you would consider to be low mileage for a car.
Although it's not a true indication of course of the engine's condition, I think first impressions count a lot - a engine that's clearly been kept washed and polished, taken care not to get scratched etc is likely to have had an owner that will also have taken care of servicing. That's not to say a tatty engine will not have been well maintained of course, just that it would be unusual for someone to take care of appearance and not bother with proper maintenance and servicing.