What would be a stable OS upgrade for my mid/late 2007 Mac Book Pro?

Can anyone advise what a stable OS version would be for my mid/late 2007 Mac Book Pro? I am running Snow leopard 10.6.8 and know I can upgrade to Yosemite but have my hesitations after reading many comments on blogs. I've started to notice the effects of Snow Leopard being fazed out and want to upgrade but don't want to kill my machine while doing with a OS thats too much for it. I also don't want to lose apps in the process due to incompatibility.

My basic specs are as follows:

Processor: 2.6 GHZ Intel Core 2 Duo Memory: 4GB 667 MHz DDR2 SDRAM Hard Drive Capacity: 320GB (27GB available)

I need to upgrade to use apps like Teamviewer 10 for example (as it's not supported on 10.6.8) but as it is my machine has slowed down and hangs despite repairing the permissions, using maintenance in OnyX, using Preferential Treatment and DiskWarrior (I've not repaired the disk in DiskWarrior yet despite my graph showing 39% errors). I just don't want to upgrade too high and completely affect my computers performance. I am correct in assuming this? Any thoughts would be most appreciated!

Thanks

Paul