Personally, I love the row 18/19 exit rows on a 757 -- always my first choice. That said, I'm pretty trim, so I don't have to worry about limited seat width from tray-table armrests. I've never been bothered by passengers congregating for the lav, but if that worries you, select seats A/B or E/F. I get priority boarding (as will you), so lack of floor storage isn't a problem. Also, I've never been cold sitting near an exit -- I pretty much ignore that on SeatGuru.

The thing I like about those seats is that I and/or my neighbors can get up and about without asking anyone else to move. I also like the e x p a n s i v e legroom.

That said, it is definitely a personal preference. SeatGuru is a great place to start and will tell you critical pieces of info (like limited recline), but ultimately you have to sit in the seat to find out if you like it or not.

Edit: The slide is a minor inconvenience. I've been in that seat before and don't find it annoying.