rename to mostRecentActivityFirst to disambiguate from sorting by when you joined a room, which this is not.

src/controllers/organisms/RoomList.js

@@ -96,7 +96,7 @@ module.exports = {
     },
 
     getRoomList() {
-        return RoomListSorter.mostRecentFirst(MatrixClientPeg.get().getRooms());
+        return RoomListSorter.mostRecentActivityFirst(MatrixClientPeg.get().getRooms());
     },
 
     makeRoomTiles: function() {

src/controllers/pages/MatrixChat.js

@@ -107,7 +107,7 @@ module.exports = {
         cli.on('syncComplete', function() {
             var firstRoom = null;
             if (cli.getRooms() && cli.getRooms().length) {
-                firstRoom = RoomListSorter.mostRecentFirst(
+                firstRoom = RoomListSorter.mostRecentActivityFirst(
                     cli.getRooms()
                 )[0].roomId;
             }