It is only possible to accept a single answer in the StackExchange system. The accepted answer will be "pinned" to the top, and this it will be the first one any future visitors see.
In general, in such a situation I'd accept the answer which I think will be more useful for future visitors. Also, upvote all the answers which are useful/helpful, not only the best ones.
If you think that an answer is so useful that it should be specially rewarded, you can always offer a bounty. (Seeing that you are talking about my answer too in this case, please don't do that. You actually can't until you get 4 more reputation points.)
When you can't decide in such a situation, it's always good to think about the bigger goal of StackExchange: it strives to be useful not only for the original poster, but also to anyone who might be googling for the same question. This is why both questions and answers can be edited by all users, not just the original posters: sometimes it's good to update them, make them more readable, easier to find, more accurate, extend them, etc. I consider this aspect of StackExchange more important than the reputation system.