I've been a customer for a number of years now and have been happy with my service. I have an iPhone 4s (w/unlimited data) and plan on getting an iPhone 5s when my contract ends on 10/14. What's disappointing is the lack of incentives for me to stay on your service. Not only do I have to lose my unlimited data, unless I want to pay full retail for the new phone, but the current plans are all more expensive than what I currently pay and you give me no deals for re-signing with you. I get the same basic deal that a new customer would get. On the flip side Sprint will give me a decent credit for my current phone and $100 to bring my number over to them and their plans are more affordable overall with unlimited data.
I like Verizon but if feels like your doing nothing to keep me here. I'll be paying more and getting less (loss of unlimited) if I stay with Verizon. Doesn't seem like a great way to keep customers. No incentives for loyal customers is not a best practice, IMO.
If Sprint is a better fit for you, it seems you would be crazy to stay with Verizon. I certainly am all for going with the provider which provides the service which best suits your needs. If Verizon and Sprint BOTH suit your needs yet Sprint is considerably less expensive, it seems to be a pretty easy decision.
As rcschnoor stated if Sprint will work better for you then by all means go with them. Keep in mind that their unlimited data is only unlimited while you're on their network. If you plan on travelling or are not in a direct sprint network area then you only get 100mb or 300mb (don't remember which) and if you go over that then you are subject to extremely hefty overages.