I went to an art store and got one for 20 bucks. Can't put stickers on it but will fit underneath your seat if you commute if their isn't any space in the overheads which is great!
During IOE, I bought one online from some pilot vendor and I didn't know what to buy. So I got one that I thought was good. Welllllllllllllll, lets just say my IOE capt laughed when he saw how big it was. Yes the 170 has a lot of room and I had to maneuver the seat right to get it in the space, that's how big it was.
Good Luck