Both the Mirada and the Allegro are entry level coaches, but if you look closely, you will see the Allegro is definitely a cut above the Mirada. As a current Tiffin owner, going with the Allegro would be a no-brainer for me. Not only is it a nicer coach, it is much bigger (35', 4 slides vs. 29', 2 slides). Not only that, but Tiffin customer support is legendary.
The other thing to look at is the cargo carrying capacity of both coaches. A sheet showing the CCC should be posted inside a cupboard somewhere. Unless you really are minimalists, you will need AT LEAST 1,000 lbs per person. Our CCC is around 3,000 lbs, and we are using up every bit of it. The Mirada is on a 20,500 lb GVWR chassis while the Allegro is on a 22,000 lb GVWR chassis. However, the Allegro is longer and has 4 slides so I suspect both coaches have a marginal CCC for full-timing.