Link to the Diamond website where they publish NTSB [US] accident stats for SR20/22, DA40/20 and Cessna 172/182.
Diamond Aircraft
Not sure what conclusions (if any) might be drawn from the figures, even normalised by hours flown/fleet size.
Clearly the SR20/22 are faster than DA40 (typically 133kts at 8.5gals/hr - AVGAS), both of which are faster than a 172.
I would imagine that there are not many SR20/22 used for training; clearly 172s and DA40s used a lot for this (so maybe lots of hours flown with an instructor on-board in reasonable weather -> accidents less likely).
No BRS in the DA40; option to fit in the 172. However, according to this article
Rediscovering The Diamond DA40 - Plane & Pilot Magazine | PlaneAndPilotMag.com the full-stall descent rate in a DA40 is actually lower than the descent rate in a SR20/22 with the BRS deployed.
I have been told that there has never been a post-crash fire in a DA40 (aluminium tanks between the spars) whereas the SR20/22 is a wet wing.
Never flown an SR20/22 but the DA40 is very docile (in my experience more than a 172 in a stall).
26G crash cell in the SR20/22 and DA40 but not in the 172.
Clearly the SR20/22 offeres a lot more than DA40 and 172 in interior space and other things [and can of course cost a lot more], but that is a different question....