What's your favourite gear ratio?

building up a singlespeed for my brother for his chrstmas present (first ever foray into building a bike) and i've gone for 38/16.. will this be ok? I dont think he has ever done any excercise before..

That's pretty spinny (I used to ride 39 x 16 and found it a bit silly riding fixed) but should be ok if it's a freewheel as he can coast.