Veneers colors -om2 or om3? I'm confused by the shades name. Are they different brands/materials?

The shade you choose is very important, and how many teeth are being veneered is also a determining factor. If you are looking for a VERY white shade- you must do at least 8 teeth in each arch, otherwise it will show the Difference  too much. 

The lightest ‘natural shade is a B1 ( vita classic) or 1M1(vita 3D) shade guides. In Hollywood white shades there is OM1 -OM3. Where 1 is whitest. There is another brand guide that uses BL1-BL4, again where 1 is the whitest. 
My preference is either B1 or OM3

All these shade tabs, sometimes us Dentist even get confused.  Just stick with your dentist’s shade guide choices (0M3 or 0M2). I have many patient select 0M2 brightness. I think it looks great! I don’t believe it’ll look fake if your dentist and their lab makes your veneers naturally. 

This will depend on how sparkling you want your smile,om2,is the whitest of both,and can give you that smile you are looking for,all patients are different and will depend on your job,and how you are,if you are on sales,bussinesman,and talk to many people ,or you just want people to envy your smile,this is it.if you are more classical choose the 3, also leave it to your doctor and he or she should have pics of before and after from many other patients