I realize that is a loaded question, but it is not an unreasonable one.
given a hex key/iv, what mode of operation is most secure from offline attacks.
I defaulted to aes-128-cbc. Partly because of schneier's 128 > 256 article. cbc because friends don't let friends use PBE or ECB
CBC PCBC CFB OFB CTR?
Use case: multi-client and platform support, which boils down to openssl in the end
Please focus on the question, and don't try to guess the use case. This is not for a government, PCI, etc environment. Key management is out of the scope of this question.