Our 1950 cottage has double hung windows with mullions. When we did the addition at the rear of the house we opted to use single pane casement and French casement. I like the look of both. Like CRL, I'd say live without your muntins for a while and see what you think.

I like the mullions when they look authentic, and I really like the diamond ones on original windows! But for looking out the window I prefer "naked" panes LOL.

I had to look up muntin vs. mullion. If they're removable, they're muntins :)

http://blog.sierrapacificwindows.com/design-tips/window-terminology-the-difference-between-muntins-and-mullions/

Our style is transitional as well. I like the muntins on ours.

A mullion is what divides a combination of windows or doors. A divider, and usually vertical. A mullion divides the picture window from the side lights, whether casement or double hung. A muntin is used to create divisible lights in doors or windows. Even some manufacturers don't know the difference.

Fenestration Terms

Mullion: The vertical or horizontal divisions or joints between single windows in a multiple window unit.

Mullion casing: An interior or exterior casing member to cover the mullion joint between single windows.

Muntin: A short bar used to separate glass in a sash into multiple lights. Also called a windowpane divider or a grille.

Fenestration Terms

I would need to see a picture to give an opinion. To me, usually, if a house was designed with double hung windows & is traditional/transitional in style...taking the muntins off makes the house look odd. Like it is naked, or the homeowner is having the interior painted or something. A modern style home looks fine without muntins. Actually, what looks best is what the original architect drew to go with the style of house.