Clarke are the best all-round little machines out there, but they are just that - little machines. One bonus is you can get spares, IF you go to the right place.
As Nige said, what do you want it to do?
I spent ages (years) researching this, and have just bought a Portamig 211 (MigTigArc sell them, but they're more expensive than where i got mine from). There is also a Portamig 181 which might be more suited to what you want. You will struggle to find another welder that will beat the current span, number of voltage settings and duty cycle for the price of a Portamig, they're made in York, too.
Avoid SIP like the plague, especially specific units, unless you want to be fiddling with the wire feed unit all day long.
Have a look on www.mig-welding.co.uk, the forum is really helpful, I've learnt a lot from there.