2nd hand entry level MTB advice

[shouldbeinbed]

Any advice or opinions on the below bikes welcomed.
I'm browsing gumtree for a cheap entry level MTB to tootle about on and play in Clayton Vale.

there's a few interesting looking ones in £100-£150 bracket, which is all I have and want to spend.

Trek 6500
Trek 4300
Carrera Kraken xc
GT Avalanche 3.0

or a Trek 800 for £20 as its been a shed bike for a few years.

The Kraken & 6500 seem to get appreciably better reviews through google

I'm not planning on racing or doing black runs, just a bit of harmless fun on rougher terrain than my current stock of urban and foldy stuff allows.

 

[Gravity Aided]

6500 is a great bike in that range, being in the US, I have no opinion on Carerra, but have also tried GT Avalanche and found it pretty good for basic mountain biking. I think you have some good choices there.

 

[Nigeyy]

I think the Trek 800 is a pretty good quality bike -you probably aren't going to get that much more quality out of the bikes you've listed. You don't say what year your Trek 800 is, but assuming it's in decent condition and has the more common 1 1/8 steerer, I'd say clean it, lube it, and buy the best front fork* for it that you can. You may be able to get a really good deal on some forks.

*assuming you are comfortable doing the mechanicky things to fit it yourself