i'd say 6.x flavors are better, you get all the features you could have in a 5.x but also add the unified mobility and some stuff like the call forward unregistered from CUCM 4.2(x)
you no longer need to worry about OS and CUCM updates separately as they're done together now, CSA integrated, more security with the linux appliance.
not sure exactly what your worries about maintenance or support are
HTH
javalenc
if this helps, please rate
HTH
java
if this helps, please rate
