I'd tend to say the Moulton but am sure it depends. The Moulton's rear suspension is pretty stiff, therefor there is not much bob to be discovered there. The front-suspension is a different story - I could imagine that the Birdy could be better here but have not enough experience with the Bridy to judge on that. On the other hand "the Moulton" does not exist as there are various Models (even more over the years) using different suspensions (front AND rear) and furthermore i.e. for the front of the current TSRs there are springs of different strengths available plus the suspension is adjustable (and a lot of people seem unable to adjust it correctly). I am still amazed on how well the suspension on my TSR performs (after proper adjustment) while at the same time it is a very fast and very stiff ride. My last ride on a Birdy was a couple of years ago (so memory may lead me wrong) and while I liked the ride on the Birdy, too I'd consider the Moulton more perfomance-orientated, even with the entry level model TSR. Never rode one of the more expensive models.