It depends entirely on your style and taste.
Look at paintings at Paris' Louvre museum. Most of them have large, highly decorated frames. Now what about Flickr photos? Most of them have no frames. But some photographers have consistent, stylized frames they add to every photo they publish.
My recommendation would be to keep your photos free of frames at the beginning: it's much easier to make things worse by adding a frame which doesn't look good than to enhance the photo by a frame which actually adds value to a photograph.
Once you're absolutely sure the frame will improve your photo, and other people confirm that the photo is better with the frame than without it, then use one.