noBeing comparable to, larger than, and apparently more abundant the Galaxy class, this appears to be their front line vesssel..Yes, the D'deridex Class Warbirds are the most powerful of the fleet.Warbird seems to equate to a heavy cruiser or explorer, so yes the D'Deridex is the most advanced and most common ship. The ships in Nemesis seem to be streamlined Warbirds, similar to how the Sovereign evolved from the Galaxy.Given the way the Enterprise-D seemed to think of their potential, yes
I'm not sure it's the most powerful seeing as it's practically the only ship we hae seen in th Romulan fleet
The most powerful? Yes. The most common? Not necessarily. We've only seen maybe two dozen of them. It is entirely possible the Romulans try to impress other races by sending only warbirds across the border, using these ships as a form of propaganda while the majority of their home fleets (which other races never get to see because of the neutral zone) is made up of smaller ships.
I think the poster above misunderstands the comment about the warbird being one of the only Romulan military vessels. The only Romulan warships we've ever been introduced to are the former Klingon D5 (D7?) battlecruisers and the D'deridex and Valdore type warbirds which appear to be practically the same design just with slight aesthetic changes. Of those the D'deridex clearly appears most often so it's a far safer assumption to say that it is the most common warship not the most the powerful.
There was also a Romulan scout ship, which may be comparable to a Jem'Hadar attackship or the Cardassian Hideki class. These would be much cheaper to produce and more suited to patrolling/anti-piracy ops and could also escort a warbird. I would agree that the D'Deridex is the most common of the warbird classes but I believe all warbirds combined comprise only a minority of the entire Romulan military fleet, with scout ships and some kind of light cruiser mostly being kept within the borders of the empire.