Kevlar for mains and Leyona for crosses can last for months. Most people say it's like hitting with a board, but I feel that I have not lost any feel and it last for ever. I use to break any string withing two days of hitting. With the Kevlar combo it can last for a good month. Try it out. Also Big bangers is the way to go too.
I've been stringing the juniors around here in SoCal with a Poly called Topspin Cyberflash and the results have been great. They like that they can hit out and still maintain a high degree of control and spin without sacraficing the power they like. For the better players wanting more feel I cut it with Tecnifibre Multi-Feel or Natural Gut. Keep on stringing in the FREE world!
For those who string their own sticks, why would you need a poly that lasts "forever"? I string my stick every 2 weeks minimal because poly goes dead fast anyway. There's no reason to keep the polys on too long since they go dead even if you don't play. IMO, I use poly (for mains) so my chances of breaking are low vs synth, but I've never broken a main since using polys. I use synth crosses for spin. I just hate stringing with polys! They are a pain since you don't want to bend them to much. I am looking for a "soft" poly that's not expensive. I am using Cyberflash, but wonder if there's a better string. I'm a heavy topspin baseline hitter and can rip winners from anywhere. Thanks for the tips!