A few points to help determine your solution:
99.99% availabilty means you can have 52.5 minutes downtime a year which should incorporate planned as well as unplanned downtime
For unplanned downtime the following are ranked with longest to failover first:
- IBM HACMP
- VCS with IMF (immediate kernel based monitoring as oppose to poll based)
- SFCFS (no need to import diskgroups and mount filesystems)
- RAC (with ASM or SFRAC) - same as 3, but also don't have to start Oracle
However you need to also consider unplanned downtime - so for example Oracle RAC may (I am not an Oracle expert) require more downtime to upgrade than stand alone Oracle in a cluster.
All of these should give you 99.99% availability so if you don't need 99.999% availability then you can probably avoid the high cost of RAC.
If your Active-Active cluster is SAN connected then you can use standard SF mirroring which is a standard option of SF at no extra cost (although Enterprise version is preferable to give fast resync of mirrors)
If your Active-Active cluster is ONLY IP connected, the you can use Symantec Flexible Shared Storage (FSS) Mirroring which is a version of SFCFS which mirrors over IP, and also gives you faster failover - this requires Enterprise Licence
I am sure not sure of the capabilties of EMC Vplex, but almost certainly, both array would need to be EMC and probably the same model, but with SF, you could change one or both arrays and SF mirroring will still work fine (you can even migrate to new array, completely online with no downtime)
You can use VVR, Oracle DataGuard or EMC hardware replication - (use link Gaurav provided for comparison of VVR and ODG)
Mike