Depends on what you call "top". Pastels will likely be the most popular BP morph ever. I don't see any other morph taking that role... they are a visible mutation which most anyone can afford.
As for number of crosses, I think the IMG could be equally as crossable as a Pastel one day. But it's hard to find a cross that doesn't look better when mixed with a Pastel... at least one that would be better with an IMG.
