looking to fit 2tb drives in my Duo v1 to replace 1tb ones

Take a look into HCL list: http://kb.netgear.com/app/answers/detail/a_id/20641

Thanks for that.

I have seen the list but was wondering if there were any prefered ones or ones to avoid.

Always a good idea to browse the forum for the specific drive models before you buy.

I am going with WDC red myself, with good results so far. Though my v1 NAS (duo and NV+) are not running them yet, just my pro.

If your buying drives for a NAS, and you want longevity, the WDC Reds are (at this time) the only real option. Seagate are having a bad time with manufacturing / Firmware issues as of late, and I wouldn't trust anything they make in something critical like my NAS at this point in time. They've just had one too many "issues" for me to reccomend them.

On the other hand, the WDC Reds are intended for NAS usage. They will cost slightly more than a standard desktop drive, but your buying piece of mind. I don't have any - yet, but I will be getting a set as soon as I can.