Since many of the OKWesters think that every view is a good view, just asking for non-smoking isn't a bad bet.
If you don't mind some steps, lots of people prefer the upper floors - sometimes a little better view (but then you can't easily feed the ducks) and a little less noise.
Generally, the way it works (or so I was told a year or two ago) is that 4 or 5 days prior to a particular arrival date, reservations are arranged in terms of date - oldest reservations first. Then within that, medical requests have the highest priority, followed by smoking preference, and then any other request has equal priority (which basically means by date).
The problem is that there's no real "look-ahead" function (in fact there may be if the same person handles room assignements from day to day and actually does "look-ahead") - hence even medical requests may sometimes go unmet because people have been given the needed rooms (even the day before) and haven't checked out on that particular date; those people may or may not have needed the room in question, and a suitable alternate rrom may or may not have been available (a truely complex problem). Another problem is that sometimes the front desk will re-arrange things for people at check-in (squeeky wheel gets the grease syndrome) - causing a ripple effect thru many pre-assigned rooms; and something that gives the somewhat mythical (depending on who you talk too) "room controllers" ulcers.
As a result, the simpler the request, the better - but sometimes even just asking for something like non-smoking (or smoking) may not be an option when you check-in. Then, it becomes a matter of how important it is. For us visiting at Christmas, we'll take whatever GV we get, but will be willing to pay the price to change rooms to a GV with an elevator when it becomes available because of a wheelchair in our party - I figure my dad and I can walk the wheel chair up and down steps for a few days if needed (we've done it before and we haven't lost a wheelchair yet!).