There is nothing ill to be said about bouncing from one manuscript to another. Eventually one of them might steal you away from the others. You have to listen/feel for that magic. The proper story will call out to you and, if you find yourself in a white-hot fit of inspiration and typing agility, go hard and fast, for surely that is the one that wants to hog your time. Stories are like unruly little kids vying for your attention. Some are loud-mouthed, some are shy and timid, looking at you with soulful, watery eyes. Consider which one makes you feel happier when your in it. Consider which one seems more commercial. Consider which one would YOU like to read. Consider which one is more mapped out and would be an easier trek. Hard choices. But just keep writing, even if it is touch and go from one to another. Heck, eventually they might All get done.
Causes Chris Stevenson Supports
Ophra's Literacy Program. The Science Fiction and Fantasy Writers of America. Absolutewrite.com.