I would say that yes, Wishes at MK is the best fireworks show. Wishes usually runs at 9 or 10 depending on the night. The times guide will list the showtimes for every night during the current week, and they usually have the same information on the calendar section of the resort web site several months in advance. The offical calendar can be found here:
http://disneyworld.disney.go.com/parks/magic-kingdom/calendar/
Use the controls on the page to navigate to your month. Click on a date in the month and you'll see the schedule of events for that day, including the time for Wishes.
The best place to watch is supposedly anywhere on Mainstreet USA. The show is built with the castle as a centerpiece, so there are certain effects you won't get by watching from elsewhere. I've actually never seen Wishes from here, opting instead to watch almost every time from the bridge linking Tomorrowland to the hub. From this vantage point, the fireworks appear to the right side of the castle. However most people who haven't seen the show don't realize this and they all end up jockeying for a spot with a view of the castle. There's a section of the bridge to the Tomorrowland side of the center from which the view of the castle is obscured by a tree, but with a great unobstructed view of the fireworks. As such this section tends to be avoided, and you can therefore often walk right up to the railing just a few minutes before the show. As a bonus, the wire carrying Tinkerbell on her flight runs almost right over your head.
As far as seating, the only place that comes to mind is Tomorrowland Terrace. I've never tried to watch from there, but it seems to me like you should be able to see pretty well from the outermost tables in the seating area for the noodle station. Anywhere else, I wouldn't recommend sitting, as you'll be surrounded by people who are standing up, and therefore obstructing your view (if not stepping on you).
As far as getting out, timing is probably the most important thing. I'd suggest first and foremost that you give it a little time for the crowds to thin out before you leave the park. Most nights during high season, Wishes is both preceded and followed by performances of Spectromagic. People tend to leave in large numbers at the end of each performance. The key is to wait a while after Wishes is over, but to get to the front of the park before Spectro makes it impossible to do so. If Wishes is held at closing time, which is often the case, it's a little easier, because you don't have to try to time it just right. Just hang out and stroll around for a little while until the crowds thin out.
If there is a parade about to start, the street will be almost impassable, particularly with a stroller. Cast members will by trying to keep the street clear, and guests waiting to see the parade will be lining the sidewalks. Here, it pays to know that all the shops along the right side of Main Street (as you're walking out), from Casey's Corner all the way to the front, are all connected. While it obviously gets congested in here too, it is sometimes easier to make your way out from the hub through the shops rather than down the street. Not to mention the fact that you can, well, shop.
When you get outside, don't be fooled by the fact that the resort monorail line may be much shorter than the express line. They seem to run quite a few more trains on the express side, plus the resort trains make three stops that the express trains don't make, and as a result the express monorail is almost always faster even when the line is quite long. I've seen three or four express monorails arrive and depart without seeing a single resort train pull into the station.
Once you get out to TTC, there's really nothing you can do about the tram line. I prefer to park where I can walk in, but you don't usually get a choice on where you park. The only advice I can offer here is to pay attention on the tram ride in so you can try to figure out whether you can walk back to your car or not. On the way out, if you can walk, then do so. But most of the lot is not in what I'd consider walking distance. If that's the case, there are no choices to make. Every tram makes the same stops, just pick a line and wait.
As a general rule remember that Disney does a very good job of moving large number of people very quickly. Even when the lines seem long for things like the tram and the monorail, you will almost never be waiting anywhere near as long as you might expect.
