Best programs for editing subtitles?

[Bsmooth]

I like I can switch them on and off on a bluray. But on a MKV file its not so easy, sometime I just have to leave them on or have them forced just to see them. If thats the case whats the best software to adjust there size and position without screwing around with the sync of them to the video. Sometimes they are huge and I would like them to be as unobtrusive as possible.