The month of January is mostly a slow month at Walt Disney World and while some may enjoy shorter waits on the popular attractions, I enjoy taking some time to meet the characters and Hollywood Studios has a really great assortment of characters you can meet.
Despite the lower crowd levels, the wait times for some characters can remain high and there's a strategy to see them that I like to follow. Given that the lines for characters are relative to the crowd levels of the park, this guide should work year-round, you will just need to adjust how long of a wait a "short" wait means.
Some characters are easier to meet than others and that's because their lines don't usually get very long, or there are times of the day when it's definitely easier to meet them. Given the wide assortment of characters you can meet in Hollywood Studios, there's usually a few characters to meet with a short wait.
Ever since Winnie the Pooh moved into the Magic of Disney Animation, his wait time has been quite short. It's funny to see his queue with just a few people while literally 20 feet away Mickey Mouse has a line that extends out of the queue area. For whatever reason, Winnie the Pooh is easy to meet especially in the morning hours when most guests haven't made their way through the Magic of Disney Animation.
You can find Mike and Sully from Monsters Inc near the Backlot Tour and they are also easy to meet in the morning hours. Just like Pooh, most guests haven't made their way to this area in the morning hours so often you'll barely have a line here until lunch time or so. Be sure to enjoy the queue, it has some great gags hidden throughout!
Another group of characters that are best seen in the morning are Lightning McQueen and Tow Mater near the exit to Muppet Vision 3D. Just like Pooh, the Cars characters line can be signifigantly shorter than the Phineas and Ferb meet located a few yards away. The line for Cars is usually short throughout the day and you can save this line for even the afternoon without fear of a very long line.
One of my favorite characters to meet are the Green Army Men on Pixar Place and while Pixar Place can get very crowded with guests, it's usually pretty easy and quick to meet the Green Army men that walk through the area. They don't have a dedicated meet area, they simply wander through the area and pose with guests. However, without a formal line, there's no long wait either and these guys can be a lot of fun to pose with.
There's no doubt that the characters with the longest lines tend be the "fab five" of Mickey, Minnie, Donald, Goofy and Pluto (with Chip, Dale and Daisy thrown in for good measure). These characters are usually found in front of the Sorcerer's Hat and because of their location in the front of the park that is easy to find, long lines can develop quickly. If you can, it's best to time the line so that you hop on line as soon as the character returns for their next set. That is easier said than done (sometimes you'll find a line of guests that follow the character from backstage to their meet spot) but it's something to consider.
Over in the Animation Courtyard, the Disney Junior characters such as Handy Manny, Little Einsteins and Jake have their own long lines. The best time to see these characters is when there's a Disney Junior show going on. The worst time to see them is when a Disney Junior show lets out and the entire throng of toddlers descends upon the character lines. If you see this happening, come back again later.
Buzz and Woody are located across from Toy Story Midway Mania and they may be benefactors of the popularity that Toy Story Midway Mania enjoys because their lines are also quite long. Unlike most character lines, their queue is indoors (and air conditioned) so meeting them can be somewhat easier if you're not sweating to death.
There are two (well, technically 3) characters that I'd label as really, really difficult to meet. What I mean is their lines are almost always impossibly long and to see them, you'll need to arrive right when they begin for the day or you'll have to suffer through a rather lengthy wait.
The first is, of course, Mickey Mouse. Located in the Magic of Disney Animation, his line is consistantly the longest character meet I ever see. He's around all day but be prepared for a wait, even if you're going during a slow month like January. Of all the characters you can meet in Hollywood Studios, Mickey Mouse is one that nearly everyone wants to see and Sorcerer Mickey never disappoints.
While they're a bit newer than Mickey, Phineas and Ferb have some of the longest queues I've witnessed for a character. While new characters can enjoy a period of novelty where their lines are long and then shorten after a few weeks when interest wanes, Phineas and Ferb constantly have a long line that speaks to their appeal across the spectrum of guests.