The usual disclaimer: If this is your first gun and its for skirmishes then don't get a sniper rifle. You need to dump a significant amount of money into upgrades (£250-450) to make it competitive - otherwise you're just going to be outclassed in every engagement.
With that said and done: Depends on the brand, but probably the springer - gas is inconsistent and you need to be spending more than £141 to get a reliable setup - I'd imagine it's running green gas, and cooldown and the general weather effect performance massively. Consistency of shot is the number one thing you need with sniper rifles, and should be at the forefront of your purchase.
From personal experience, if you're looking for an L96 then most of the clones are fine. The Mauser is actually alright, but massively overpriced being a rebranded Cybergun. Well is probably the brand you're looking at right now, and they perform alright out of the box. I would recommend finding one without a scope and then buying your own (around about £40-80), but obviously airsoft is all about how much you're happy to spend.
One thing is for sure though: Don't go for a cheap gas sniper rifle. The consistency will be naff and the magazines will probably end up leaking after just a short while. There's also the consideration of spending more money on a decent green gas. Although this cost is negligible (around £8-16 per can), it is something you may wish to bring into consideration.
Could you provide some links to what you're looking at?