Mk1 looks a bit old now, but has a good torque-y engine especially in 1.4 versions. MK2 is more refined a bit more comfortable and has a good under floor storage area in the boot. I-shift is a robotised manual gearbox so you can drive it on the paddles all the time if you wish, but it will be sensible and change up/down when needed. I think if you use the throttle like a manual in full auto mode then some gear changes happen at times when a driver might not have performed them. In the manual you would have lifted at the change but not the case in the i-shift so can be a little jerky until you adapt your style. This is common across other makes with robotised manual gearboxes.
For the same money I'd pick an i-shift MK2 over a CVT Mk1, especially when you consider there are 15 plate Mk2s knocking around so that body will continue to look a lot newer than the Mk1 in a few years.
One last thing CVT costs more to service as CVT fluid should be changed every 2 years, if you find a bargain jerky one then it's an easy fix with a flush & refill of the correct fluid to replace the expired stuff.
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TG