I have tried both Mere Mortals and Strataframe and found them very different. Strataframe's use of Themes makes impressive looking forms but I found their tools for building business objects, stored procedures, etc. cumbersome compared to Mere Mortals. Since I use xCase to create/maintained my SQL databases, Mere Mortals suits me better since it can create all the business objects in one step including classes for business rules, defaults, etc. It will also batch create all the stored procedures for CRUD on each table whereas with Strataframe you have to create them manually for each table. Since most of my apps have dozens of tables, this saves a lot of time.
Strataframe has a lot of sample solutions and Mere Mortals is very limited in this respect. Being new to .NET, Strataframe might ease the learning curve especially since they have stated they will create sample apps for all frequently-asked questions. Strataframes use of Business Objects is more "visual" since they are dropped onto forms from the Toolbar and appear in the area below the form. The Strataframe tutorial is in VB.NET only and I like to see both VB and C# since I still haven't made up my mind which language I will use (although I am leaning towards C# for some reason). Mere Mortals has one entry for each databasekey in a config file to specify connection strings for all business objects where Strataframe specifies the connection string for each business object. All in all, they are very different but I am not qualified to say which is "better" especially since I have limited experience in .NET as well as the two frameworks. Individual's requirements are also very different for each developer.