First bike purchase in 20 years

I’ve decided the time has finally come to replace my trusty 20(ish) year old mountain bike. It was a good bike in its day and has been very reliable but I’m finally ready to join the 21st century.

I have tested a few bikes recently and think that a hardtail with 27.5” wheels is going to be best for me. I also need it to be a bit of an 'all-rounder' that I can use for everything from commuting and cycle paths, to cross-country and trails.

I don’t want to spend too much at this stage and have been looking at the 2014 Boardman Team HT 650b. It's already on offer in Halfords and I can get a further discount so the final price should be around £520. This looks like a good deal although I had originally thought I wanted to stick with Shimano components. http://www.halfords.com/cycling/bikes/boardman-end-of-season/boardman-mountain-bike-team-ht-650b-2014

I’m also very open to buying second-hand, particularly as I don't know exactly what I'm looking for. One second-hand bike that caught my eye is a 2015 GT Avalanche Expert. It looks in good condition and would cost around half the price of the Boardman. http://www.gtbicycles.com/int_en/2015/bikes/mountain/trail-hardtail/avalanche-expert.

I’ll go and see the GT over the weekend and will then decide whether to go for that or the Boardman - but I would welcome any views on which bike might be the better ‘all-rounder’ and the better purchase?

Thanks