Prior to 2012 or 2013 the Allegro Bus had a 14,600# front axle. The 60/40 suspension proportioning valves caused the front axles on some 43' models to be at or over their rating. Tiffin worked with those that complained to remedy the problem. My 2013 Bus had the heavier 15,600# front axle and it was close to max with the OEM 60/40 prop valves. Tiffin replaced them at my request with adjustable valves and installed 70/30 valves on some customer coaches. Check with Tiffin as to whether the one you are looking at has been updated. If it has, the AB would be the better choice.
Edit: 2014 was the first year of the 45' Bus. It has shorter dash which we did not like, but it gives you a little more floor space plus it's 2' longer. I think it also has a heavier steer axle due the heavier weight. About that time, Tiffin eliminated the proportioning valves completely and accomplished the weight distribution between drive and tag axles with different size suspension air bags.
2013 43 QGP Allegro Bus ( SOLD )
2000 AEV TJ