Parameter sniffing = On with Parameterization = forced. Which takes precedence?

These do not conflict. Parameter sniffing is the process that uses the parameter values when building a plan. Forced parameterization turns literals into parameters in queries.

So having both on will turn literals into parameters, but not use those values when estimating cardinality.

More on parameter sniffing

More on forced parameterization

Parameterization and sniffing are separate activities. An ad-hoc statement can be parameterized by SQL Server without parameter values being sniffed.

Paul White has an excellent blog post on : Parameter Sniffing, Embedding, and the RECOMPILE Options which covers both Parameter Sniffing and parameterization in detail with examples.