Is there an old oil change sticker that may tell you what oil has been used for the last 180K miles? If so, I would consider sticking with that.

Otherwise, like mentioned earlier, if the low temps in your area get in the zero or below temp range where you live, a 5 W 30 would be good, if the temps pretty well stay near freezing or above, I'd go with a 10 W 30.
that stated, with that many miles on the motor, some don't like the 5 W 30 very well, but if the motor is OK with it, the thinner oil makes it easier to start on those cold mornings.

Along the same lines, if the summer temps get over 90 degrees pretty often, I would go with the 10 W 30 over the thinner oil. There is nothing wrong with changing the weight of the oil between seasons.

The difference between the dino oil and the full synthetic oil or something in between the two is pretty much a personal choice, nearly all of it is good, but sometimes the motor chooses one over the other. Most of the 5 W 30 oils tend to be synthetic or a synthetic blend, and that thinner oil seems to be able to take advantages of small leaks much better.