Does it matter how the IV and XOR are applied for a single AES-128 block?
Yes there are differences.

The first one is identical to CBC mode encryption. CBC requires an IV that is indistinguishable from random to an adversary.

The second is identical to CTR mode encryption where the IV is the initial counter value; the IV only needs to be unique - but the IV can be randomized, as a 128 bit random number is unlikely to repeat.

You never want to do anything to your key other than using it for your cipher. If you want to create multiple keys, use a Key Based Key Derivation Function such as HKDF rather than XOR.



Note that generally you should try and find the best mode for your operation, and only then generate your IV using the rules for that specific mode. 

Authenticated encryption using an AEAD cipher such as AES in GCM mode often makes a lot of sense. GCM for instance generally uses a 96 bit IV / nonce instead of a 128 bit IV.