As well as the fork advantage talked about by others last night, the 13's frame is highly rated and worthy of long term upgrades, plus it does internal cabling.
But looking at Halfords again in the last few minutes, your choice has become more interesting, as the Voodoo Bizango has been reduced in a promo to £530.
Topcashback currently has a 4.2% cashback and a voucher code that reduces all bikes except old Boardmans by a further 10%!
Until I saw this Bizango update, I was going to say from the links given last night, the Aventi Mesh Deore was my pick of best bang for the buck (albeit I've just this second seen that only the 14" is in stock).
So that makes it either the 13 Incline Alpha or the Voodoo Bizango for me, if a hardtail meets your requirements.