I will say the udk one is a litle bit better.Not because im a fanboy,its because the ue4 bsp or whatever is using,looks too dark.Either way,for something like a coliseum,i loud model it by hand in a 3d app and not use bsp simply because i wont stand those hard edges.Or if you leave it with bsp,than you will have to do a lot of set dressing to hide the look.For example something like carpets/blankets on the stone for the people to seat or wood.Series like Spartacus shoud have good reference on this.