If you only want to use it with Mac then let your Mac format it as others have said.
Howver, there is more than just one choice for formatting an external drive for both Mac and Windows. There is an article about it here:http://externaldisk.co.uk/article/2012/05/14/format-my-drive-for-mac-and-windows.html
To cut a long story short exFAT can be used with both Mac and many Windows operating systems as well as FAT32. You can also get software for either Mac or Windows that can read and write the other Operating Systems favourite format, but there is usually a cost.