Op, go for blockchain.info - as in the long run it doesn't matter if you have to wait couple days to be accepted.
Other online wallets might have API with easier setups and configuration process but blockchain.info is one the best overall.
I don't have a problem with waiting a few days to get approved but I saw i need to provide domain name. I do got it but i don't want to upload stuff to my host every time i want to test/update something. That is what bothers me, can I use API on localhost ?
Anyway in last few hours i test Blocktrail API. Don't need to wait for approval, very easy to use in PHP (idk about other languages) and what I like the most you can create test wallet and use test network while developing app. I know blockchain.info is more popular, so if someone can provide more info about usage that would be great, also what are your experiences with Blocktrail ?