Order I would do the characters based on popularity and the sun, characters were out from 9am to 7pm last year:
1.-Disney SW: Jedi Mickey, Leia Minnie, Darth Goofy ,Stormtrooper Donald and R2MK. The rotate so you may start making the line for a pair and then they switch which contributes for this line being so long, also its in the sun all day and even though they put up some umbrellas, it doesnt help that much. They are by the exit to Great Movie Ride (1 hour and up)
2.- Chewbacca and Ewok: Another very long line, they go in every 20min., they come out about 5 minutes after they go in, Chewbacca is very popular, this line stays consistently long thru out the day. Its semi-shaded so that helps. They are at the Speeder by Star Tours. (1 hour and up)
3.- Darth Vader: Its the Dark Lord what more can I say. The good thing is that its under roof all day but, again, it stays long all the time. He meets by the exit to Backlot Tour (45min and up)
4.- Darth Maul: His line gets some shade during the day, he meets next to the entrance to Backlot Tour. (30 min. line)
5.- Bobba and Jango Fett: very little shade for them, they also rotate, they meet by the entrance to Backlot Tour (30 min. line)
6.- Clone Wars. Ahsoka Tano, Asajj Ventress, Rex and Cody: the line is in direct sunlight all day and they also rotate. They are by the Premiere Theater (Muppetvision 3D area) (30 min line)
7.- Jedi Council. Anakin Skywalker, Mace Windu, Shaak Tii and Kitt Fisto: they are by the San Francisco mural and get sun during the day. (30 min. line)
8.- Queen Amidala: the poor Queen is in the sun all day, she meets next to Sounds Dangerous (20 min. line)
9.- C3P0, R2D2, Luke Skywalker and Princess Leia: They rotate and it takes time to get all four of them but the good news and why I leave this one for the end is that they met inside the Merhandise tent last year. A/C makes a huge difference.
There are roaming characters that are around the park. These are easier to get a picture, you just jump in.
Around Star Tours you may find the Cantina Band
Around Premiere Theater you may find Jawas, Clone Troopers
Around Backlot Tour Stormtroopers, Tusken Raiders, Gamorrean Guard, Aurra Sing (my fave) and Zam Wessell
This year there are rumors we might see Chip and Dale as Ewoks, talking to a character CM during May the 4th he said that they should have a separate line
also pictures from the May the 4th event we saw Greedo meeting outside Backlot Tour. Like Berlioz said he makes an appearance during Hoopla but has never been out for M&G.