you'll have to decide if you want aluminum or glass. 20 to 21ft. since you mention the detroit river I take it you plan on jigging/handlining the river and trolling lake erie. you can get by with an 18 or 19 fter, but the extra room/comfort of a 21 fter and being able to span waves better with the 21 would be alot nicer. are you buying new or used? glass tends to be a much dryer ride, but when it's really rockin out on erie, give me tin. the transom lifts alot faster = less water in the boat/less chance of filling with water. I run an 18 ft aluminum I have setup to do it all ( would like a 21fter) and it's always gotten me back even in 8+ fters thru many tourney's. you have to know how to run what ever you get, but there's always a chance of a rouge wave and that changes everything..quickly. don't under power if your going to fish erie. decide what type of layout you want/need. sit in plenty of boats, look around and think about where everything is mounted, stored etc etc. then go shopping