Go with the static methods.  Why create an object if you don't want or need
to store state?  And if you do allow a singleton object, it's only a matter
of time before someone does add data to the class, and then you may have
synchronization, deadlock, and/or scalability issues.

To answer your question, the static methods will be faster.  When you call a
non-static object method, the first thing that happens is that the "this"
pointer is pushed onto the stack.  There is no such step when calling static
methods.  Of course, the performance benefit is likely negligible in an
n-tier world - things like network hops make saving a few cycles irrelevant.
So this decision ultimately comes down to what is easier, safer, and cleaner
to implement and maintain.  Client code calling static methods is generally
easier to read than code calling non-static methods, and it's a better OOP
design.

-Bill