well for a start some of them are overlockers / quilting machines, which you definitely don't want! Key things to think about are:
- are you at all familiar with sewing machines? if not, then get something that is quite simple but will help you with complicated things.
Also how often are you going to use it? don't spend a fortune on one, and I personally wouldn't bother with a computerised one, they'll just be more complicated to fix if it breaks. plus all these modern domestic machines have so many different stitches but you'll probably never use half of them!
Some of those argos ones look ok, i would go for a mid-range price and brand-wise I like Singer and Husqvarna Viking (Swedish not sold at Argos though!).
I would advise you go and have a look at some though. john lewis normally have some on display and i think you are allowed to try them out too. also specialist sewing shops would be able to help you, even if you end up going back to argos to buy one.
another option is a recon 2nd hand one. thats what i have, its old, heavy and only goes forwards, backwards, side to side and i love it!! good luck