Depending on your need for speed and (of course) budget there are a few suggestions:
A1 printers:
Epson Stylus Pro 7450 (4 ink tanks)
Epson Stylus Pro 7880 (8 ink tanks - up to photo quality)
Canon iPF610 (A1 print in 33 secs)
All these are A1/24" printers.
I use an Epson Stylus Pro 7600. Not in production anymore, but works great for me. I've got a roll of Glossy Paper so if needed I can print HQ photos for events, 3D models of boardrooms and such. Just to impress