The Ravens official site is reporting that WR Marcus Smith looks like the favorite to win the 4th WR job:

Smith’s solid play has made him the primary candidate to be the fourth receiver. “Comparing to a year ago, it’s night and day,” Harbaugh said of the former fourth-round draft pick. “We talk to our guys about making the most progress between their first and second year, but Marcus just goes to work. “The thing about Marcus is, you see a little bit of improvement every day because he works as hard, or harder, than anybody on the team every single day. So, you start adding all of that stuff up and you watch him out here at practice and you guys are like, ‘Wow, this guy is really playing well.”