Welcome ErrantTemplarr.
I guess what you're trying to do is make several caps and pick the best, right? Or do you mean previews for videos?
MP Classic is a pain to cap with. It doesn't seem to cap on the same frame as you pause it and takes forever to render the cap. It is great for those previews on videos though.
VLC player is really the easiest free software to cap with. If you want to make series of caps you can do so with whatever hotkey you have set for it. To make it easier you can slow down the video to 1/2 - 1/4 speed and snap away then go back and pick the best ones. For pay software if you have Nero or certain versions of PowerDVD you can also do the sequence caps and go back and pick the best ones.
I've found the ideal way to get an perfect still is to pause right around when you want to take the still and frame advance until you have the shot you're looking for. You can do this with VLC, Nero, & PowerDVD. The frame advance also allows you to get a shot that isn't blurry where with the sequence capping method you make get caps a blurry cap from compression and motion.
Just some more notes here, I like to set the VLC hotkey to something easy like "C". I think the default for C is crop so you have to change that first. Also with VLC player, make sure to set your deinterlace setting to auto so you don't get lines in your caps. See which interlacing method gives you best results with your video source, and you're on your way.
ErrantTemplarr! 
