It depends largely on what position you play, which you can handle most comfortably and effectively, and the design you understand best. Shockers are -THE- back player's gun hands down. They're steady to aim, very quiet, never break or chop balls EVER, but a bit large and heavy. Impulses are great in that they are lighter and still have many of the Shocker's strong points with a very nice price, but are more suited for front players. Matrixes I have not personally shot so I can't give a competent opinion on them, but I can say that I don't know that many people that know their design well enough to be able to help you with troubleshooting.
Give them all a look and see for yourself in person.