With welder sizes i always go for the best you can afford , for a good all rounder you want to be aiming for a 180 amp unit , i know its hard but try to stickto branded makes aswell ,

sip are ok for the hobby man and can tackle some bigger jobs aswell .,

Clarke and draper i havnt had much experience with so cant realy comment , Have a look on ebay for a second hand unit , youll get twice the welder for half the money

http://cgi.ebay.co.uk/Elland-145-Pro...QQcmdZViewItem

not a bad set .

http://cgi.ebay.co.uk/SNAP-ON-MIG-WE...QQcmdZViewItem

a snap-on set

the very top brands to look out for are

Murex ( they also make snap-on's welders )
BOC
Butters
Transmig

two other things i have just thought of that will also help you is :-

use a tip one size above the wire you are using , ie , if u are using a 0.6 wire use a 0.8 tip , if using 0.8mm wire use a 1mm tip etc , this will help stop the wire sticking if it gets a bad arc or burns back .

Not wanting to teach others to suck eggs but the correct direction to mig weld is to push the torch , ( not pull) i e start at the right hand side of a weld and traverse to the left , the torch tip should aslo be at approx 30-45 degrees to the work piece and inline with the weld .