Some says pre-stretching is better for tension lost, so the string bed maintains tension longer but some says pre-stretching causes the string to lose its elasticity, hence play worst. Whats everyones opinion on this?
To some it matters, to others it matters not. Why not try a comparison and decide for yourself? I always prestretch. There is nothing worse than falling in love with a crisp new string only have it to sag and underperform a few sessions later.
I've learnt to just avoid strings that lose tension too easily eg. vs850, bg65, bg66um. Be careful not to over do the pre stretch, otherwise you would cause the string to irreversibly go past its elastic limit. Instead I've switched to Zymax strings which have the best tension retention around in the market.
All strings have a "creep limit" - a tension beyond which they start to lose power. However, a hand-prestretch will never take a string anywhere near it in most cases. Prestretching, IME, really extends the tension holding, is I always do it.