I've had my St for a month now and just wondering what's people's opinions on the best remap? I don't want to end up having issues with warranty being void so preferably a map I could revert back to standard easy if need be (like a bluefin) I did look at mountune but seems like a ridiculous price for the gains. Thinking maybe peron stage 1+ 

If you want to keep warranty - Mountune regardless of price. You can revert back to standard but if anything with the engine screws Ford will most likely know you've been messing and will thus void your warranty.

I've heard of too many people swapping maps back to standard when taking their cars back to ford for that to even worry me. There's no way they would ever know as long as the ecu has the standard software back on should I ever need to take it in. Mountune reviews seem too flat, more like a case of a bit of extra power. I want something that will be noticeable. 

If it was a serious enough issue they can tell it's been remapped but you should be ok with whoever you go with.

if I wasn't going for Mountune then I would go in this  order, Collins, Peron, Revo, there are others, GGR (who use superchips bluefin), JW racing,  pumaspeed or independent mappers that advertise on Facebook etc. Depends how much power you want and how little you want to spend.

I can recommend the Collins stage 2 map as I have it myself. I have also heard good things about Peron too. Both allow you to revert to stock if you buy their OBD tuners

What power you running on the Collins map? And how much was it?