The DirectAccess capabilities between UAG and Server 2012 are almost all the same. The advantages that Server 2012 DA has over UAG DA are when using all Windows 8 client computers. If you are, then you get the capability to provide multi-site DirectAccess (multiple datacenters with failover). This only works for Win8 clients though, not Win7. If your clients are Win7, the differences in capability between the two solutions are very slim.
However, going with UAG gives you not only DirectAccess capability, but also the ability to publish UAG portals (SSL VPN portals) at the same time on the same box. So you can run DirectAccess connections as well as publish portals for OWA, SharePoint, RDP, SSLVPN, all kinds of different things. This can be a nice way to get users connected from non-DirectAccess machines like home computers or kiosks.
You mentioned SharePoint, ADFS and reverse proxy. These are all things that UAG can publish for you. Server 2012 remote access can NOT.