Once again, Berkshire Hathaway Inc.'s annual shareholder meeting stirred up speculation over who will take the reins once Warren Buffett decides it's time to retire. And while he didn't reveal any names, the Oracle of Omaha did announce at Berkshire's May 4th event that the board is "solidly in agreement" on who his successor should be. Some railroad industry insiders and observers like to theorize that BNSF Railway Co.'s Matt Rose is the top contender, while folks outside the business point to Berkshire Hathaway's investment insurance chief Ajit Jain as the next in line. The Wall Street Journal recently reported that, in addition to Rose and Jain, other possibilities from within Buffett's inner circle include Charlie Munger, Berkshire's vice chairman; Gregory Abel, chief executive of Berkshire's MidAmerican Energy Holdings Inc; and investment managers Todd Combs and Ted Weschler.Who ultimately will get the top job is anyone's guess, so why not join the guessing-game fun and answer this week's poll question on www.progressiverailroading.com. Also, in response to this blog, you're welcome to post your thoughts about who the most qualified candidate might be — even though it's hard to imagine that anyone really could replace Warren Buffett.