Any electricians in the house? Wire size question.

I'm going to be feeding a 240V, 100 amp sub panel for some camper pads at a property. The distance from the panel to the sub-panel is 250'. I will be using aluminum direct burial wire.  

What size wire is recommended? The calculators I've found suggest 1/0 for a 5% voltage drop or 2/0 for a 3% voltage drop. With modern electronics, I don't see where the difference between 3% and 5% would matter. 

There is about $140 difference between the two sizes. 

Thanks.

No one has ever said "boy I sure am glad I ran the undersize wire"

I would run 2/0 considering all the struggle with pulling 250 feet of wiring, terminating it, the cost of the boxes, breakers, outlets, everything else, and only saving $140.  

I am also the guy who wires everything up with 12 gauge wire instead of 14 gauge other than dedicated lighting circuits.  Juice isnt worth the squeeze.  

I would actually upsize it to 3/0.  Just in case you want to add something else down the road.

Or hell - 4/0 at that point.  Or a small nuclear generator, 

Then there are us 70+ guys that don't use aluminum....  Go big or go home.

Aluminum is fine if you install properly and maintain.

Just to chime in my .02. The code has a limit of 3% voltage drop from feed to last device. So right there both wire sizes are to small if you are basing it on there voltage drop alone.

Now if your going direct burial are you putting a bed of sand down under and on top of it? Seen a few failed runs from sharp rocks cutting the casing and ground water corroding the wires.