Prefer Irena...
Or Eirena. Heheh. I like it. I've been on a vowel-names kick, though, and here are some other I names I like:
IrenaIrisIolaIlena
Irisa (don't know if it's a real name, and wouldn't use it as such, but it's an alternative to
Iris)
ImogeneIreneIsadoraIsabel