Secure and cloud do not
If your data is in the cloud, it's by definition not secure: anyone can access it, if they spoof/steal/copy/guess your credentials. If security is an absolute pre-requisite, keep your valuable data off
Nor is your own box secure if it connects to the Internet - an airgap is the traditional solution to avoiding data compromise over the network. However this is seldom practical.
In the real world, Dropbox is the touchstone that others have to beat. What is better about SpiderOak?
Oh, yeah, I should add - data security is as much about retention and recovery from loss as it is about leakage. How does SpiderOak fare in the "We'll still be in business this time next year even if our server farm gets hit by an earthquake" stakes?
"Klinger, do you know how many zoots were killed to make that one suit?" — BJ Hunnicutt, 4077 M*A*S*H