Root a Sim free S5 ? or purchase Sony Z3

[waxwobbler]

Would I be crazy to root a brand new phone ?

I have tried a Galaxy S5 and it does seem to be laggy, more so than a friends Sony Z3. I like the removable battery of the S5 but not so keen on TouchWiz. So but the Sony or buy the S5 and root it then remove apps or install custom rom.

Does anyone have specific instructions for an S5 that was would be purchased in the UK, SIM free ?

Thanks