Specifically, both tools do ETL and do it well. Alteryx has better out-of-the-box support for more connection types, and also better out-of-the-box support for integrating advanced analytics into your workflows. Informatica might have (costly) add-ins to talk to older, obscure (basically obsolete) data sources if needed.
More generally, Alteryx is newer, shinier, faster, much easier to use, and just as important: a much, Much, MUCH friendlier company to work with. In that light, I cannot recommend Alteryx highly enough, but I also have significant reasons for recommending anything over Informatica, which are so frosty that I will not share them on a public forum. Feel free to IM me if you want the sundry details.
