Most windows come set up today for picture framed trim, however it is easy enough to convert to an interior sill which is how all my historic reproduction customers request their windows. A sill gives more room if you like to have nick nacks on the window sills, or if you put Christmas Candles in the window. A picture framed approach is a more contemporary look. as far as the outside goes if you want a sill appearance yo can do it one of several ways. 1) order the window with a subsill applied and they should come in you choice of thicknesses. 2) Order the standard window and apply a flat or brick mould trim on the top and sides with a sill profile on the bottom of the window. This can b in wood, a composite material or a clad material.

On the inside you can apply a window sill in one of two ways. One is to just apply a sill cap over the existing Jamb extension. Another way is to take the bottom jamb extension off and make a sill cap to replace it, or some companies will let you order the window with the jamb extensions on three sides only this is the easier way with companies that wrap their Jamb extensions on.

Basically it depends on your taste today whether you have a sill on the window or not In most cases the picture frame approach works very well

Thanks so much for your input. I'm leaning toward picture frame approach but will visit homes/window stores to see how they look.