What is the difference between SQL Server 2012 SP4 vs SP3 with CU-10?
2012 SP4 contains all the same fixes as 2012 SP3 CU #10, and was basically just a rollup to release a final service pack. The only differences are going to be:


build number will be higher
longer end of life
potentially better chance of servicing for a security issue in the future
easier slipstreaming


Personally I would go with 2012 SP4.