Most secure 32-bit block cipher
If you care about security, and don't care much about performance, you might consider a Format Preserving Encryption mode such as FF1; this is a mode of operation that uses a 128-bit block cipher to form an arbitrary sized block cipher; this arbitrary size includes a size of 32 bits.

It is believed (I don't think we have a proof in hand) that, if instantiated with AES, it is as strong as AES (with the caveat inherent with having a block size of 32 bits); hence you have at least 128 bits of security.

Performance isn't great (performing an encryption or decryption of a single block involves 10 AES operations), however depending on what your use case is, it may be quite acceptable.