I have and use the circle attachment for my Pfaff. I love it. I bought it because an extension table came free with my machine when I purchased it. It seems like either would work fine but the deciding factor would be the size of the circles. Make sure whatever you choose has a size for the largest circle to the smallest circle that you plan to make. The smallest diameter I can make with my circle attachment is about 2.5" and the largest 10". But it also came with a template so I can make something akin to a flower petal so I am not limited to just circles. I don't think a table would let you make a circle as small as 2.5".
Either way you will love making circles!