For a Singer the 15 and 66 would both work fine, though a 201 with the external motor would be quieter. A 115 would work well, too, though they're not as common as the first two. A White rotary would probably be a nice choice as it even has a bit more throat space than the 66 and the 201. Another interesting option would be a Singer 9w - lots of space and a vertical rotary setup should you ever decide to do some free motion work. Maybe a Wheeler & Wilson, too, but I don't know about needle/bobbin availability.