Hi,
What edition of SQL Server 2008R2 are you using (Enterprise, Standard, Datacenter, etc?)
If the question is if you should use 32 or 64bit it depends on your license but I would suggest using 64bit where it fits in with your licensing agreement and support ability on vCenter 6.
E.G - Microsoft SQL Server 2008 Standard (R2 SP2) - 64bit & 32bit is Supported on vCenter 6.0. however Microsoft SQL Server 2008 Standard (R2 SP3) - 64bit & 32bit is not supported according to the Product Interoperability Matrix
If it were me with hardware in this day and age I would advise you probably use 64bit.