Interpet Bioactive tapsafe (Blagdon Bioactive tapsafe in the pondsection is often cheaper by a few pence but is the same stuff repackaged).
To be honest, a dechlorinator is a dechlorinator... they all do the same job, its down to value for money and how easy it is to get hold of. Not many shops sell Seachem Prime, i can guarantee that MH doesnt. So you would have to buy it online... postage.. and packing.. being in for the delivery...
The AquaCare range is good the 'purple' Biological one is actually really efficient stuff for use in cycling a tank (it doesnt cycle the tank on its own but nothing does really) and for dosing after water changes or filter changes or if you have a nitrite spike.
Seachem Prime is great because you only use 5ml per 200 litres (50 gallons) of water. Not only does it dechlorinate but it neutralises ammonia and nitrites too.
If you have a world of water near you, they stock it.