ASM Question - Best Practice

Our application will likely use Oracle 10g (probably 10.2.0.4) on AIX 
v6, using an EMC Symmetrix SAN. The environment doesn't exist yet - we 
are at the planning stage.

The intention is to use ASM. So first question: The mirroring can be 
done within ASM; i.e. by Oracle, or we can do it at the SAN level.

Any advice or recommendations as to which is likely to be better? 
Availability and resilience will probably rank ahead of performance in 
terms of user requirements.

Thanks,
Palooka