It depends on how much clipping you intend to do, I'd go for the best ones you can afford, Lister and Liveryman are good makes, I'm sure most of the main manufacturers would have one suitable for you. Personally I don't recomment the Moser Artiko, ok if you 're doing an Irish, or blanket clip but I didn't find them powerful enough and wondered if I would finish the clip I was doing especially if it was a full clip. I didn't want that hassle, so got some liveryman 2nd hand, like a hot knife through butter
I have the Heiniger Cordless......fantastic clippers- will tackle hogging and hairy beasts as well as 'normal' horses. Very quite. Last long enough for a full clip.
I full clip an ISH at least twice if not three times throughout the winter and blanket clip a hairy cob the same number of times. If I can get near my Welshie I'll take a bib off him too. I also do their feathers about once a month, including the hairy cob as he gets cobby knee (I hog him as well).
I have the Heinger Handy at the moment but they have now died. Have been fairly happy with them but they were my first set of clippers. I like the idea of the battery pack rather than the cord but have never used Lister before.