I'm still learning to use Crello, but I'd rank it favorably against RelayThat (which I still use and like... a LOT). Why? Because Crello offers a far wider range of templates for many more purposes.

Crello offers many more bells & whistles, so the learning curve is steeper, but I think it's time well spent.

I'm using this with PromoRepublic to schedule a series of posts in advance. I really like Crello, and recommend it as a very worthwhile investment.