This really comes down to what model railway experience you have. The RTR model should work out of the box (I'd suggest testing it in the shop if going to a bricks and mortar outlet) the kitbuild will need work: if you have done this before in another scale then 'pays your money, makes your choice'. N gauge size mechanisms are fiddly IMO, but it may be they are fine for you? Again if buying over the counter, have it test run in the shop.