Jeff,
A good friend followed me into iron cookware collecting by concentrating on Favorite, building a large and varied collection. The companys' roots go back well before Griswold (as the W.C. Davis Co. in Cincinnatti) and they folded in 1933 or 34 in bankruptcy...but their patterns were acquired by the Chicago Hardware Foundry so there is some continuation to the line of Favorite pieces.
Favorite would have to be third behind Gris and Wag in the number and quality of pieces they made. I don't think they will ever be the equal of those two other companies in collectibility but you can't go wrong with getting some of their pieces or even concentrating on Favorite. They made a number of pieces that nobody else made and most of their quality was excellent as was their style. They made skillets in sizes 0-14. They made French Bowls which nobody else did. They made the largest popover pan of all. They made a good variety of gem pans, pots, bowls, loaf pans and more. They put blue porcelain on a whole lot of their line and it's a fantastic blue. I just received an ebay grey porcelain covered French Bowl. Never have seen the grey before though and they had a cream porcelain.
I think Griswold is the most popular due to several reasons; the number, quality, variety, and style of their pieces and the books and catalogs available. Wagner follows noticeably behind and Favorite is somewhat lost behind those two.
I think highly of Favorite and anyone who collects it can't go wrong. If you come across a piece marked THE FAVORITE, it was made not by Favorite Stove & Range but by another company; Columbus Hollow Ware Co. of Columbus, O.
Steve