The 7ER category includes both the 757, and 767-300, which is a widebody. Not sure how much longer it'll be around or doing any international flying. So if you want to jump right in that's what you should bid. Outside of that it takes more than 2 years to hold any widebody seat (330, 350, 767-400), so your seat lock won't be an issue. There's a chance that WB spots will keep going more junior but it hasn't happened yet. From an ease of training standpoint flying the 320 for a while will make the 330 training a breeze (so I've been told).