You can get all the user's videos and get the latest date:
var videos = new YouTubeRequest().GetVideoFeed(userId).Entries
DateTime lastUploadDate = videos.Max(video => video.YouTubeEntry.Published)
To get the actual video's title:
var lastVideo = videos.Where(video => video.YouTubeEntry.Published == lastUploadDate).First();
var name = lastVideo.Title