The RTS, actually. I've got RTS, 137, 139, 167 and RX, and it's the RTS I like least - it's just too heavy for my taste. That said, I don't like using the 167 in manual, as it suffers severely from "1980s crazy control syndrome". The 137 and 139 I like very much indeed despite their bargain status, and the RX is so smooth and silky, if a little over-complicated at times.