I'm about to go on a rant here so be a ready....
To start off with, to enter a competition with the hopes or goals or winning is totally fine and healthy. You should want your work to do well and if you honestly have faith in it, then shoot for the stars! To ask around to find out which competition would be easiest to win because you're so set on a prize makes me literally sick to my stomach. If you're only submitting to the con in hopes of winning shiny prizes and making the crowds love you then I'd like to offer a loving middle finger.
Personally, when I enter any kind of contest these are the things that run through my mind.
Is this a con I plan on attending? I refuse to be a troll and send out to every major con out there in hopes to accumulate awards and recognition. If I'm going to attend the con and there is a chance of me making finals or it getting shown, even in overflow, I'll enter. I worked hard on it, might as well. It's always fun to see your video played on the big screen.
Another sub-question with answers branching off of the previous statement:
If it's a con that I'll more than likely never attend, why am I submitting to it?
1) Someone I know is running it and/or going to attend and they personally asked me to enter in order to support the contest or they just want my video to be there also.
2)The contest hasn't been receiving a lot of attention or they wish to gain more recognition but require more entries. And even then, only if I have something that hasn't been sent around to every other con and the circuit and has officially become a troll will I send them a video.
3) For the competition! There are certain cons that I submit to just because they were the first I had ever competed in. Not with the hopes of winning something or lots of people looooooooving me but with "I hope I do well and I hope people enjoy this a lot. If I win that's just a plus!

" on my mind.
Now for the lovely topic of trolling~
I understand that if your video is bowling people over at contests and hell, let's go ahead and even say that I was taking a jab at "Ouran High School Never Ends" with that last bit, it's NOT a good idea to send your video to any and every con you can.
It's great if people enjoy your video and kudos if you win, but in the end, I want you to think of the competition and the crowd when you submit a video that's just rolling in awards due to sending it out on massive level.
If you know you've got a trump card video that's been lapping up awards like malnourished kitten with a bowl of grade A milk then what's the point in competing? Congratulations, with your attention whore video that you just sent to a con that you'll never even think about attending just knocked out the hopeful kid who put his heart into a vid he made specifically for that con.
Ever have your heart crushed by a heavy hitter that boggles your mind by the fact that the editor even thought about submitting to this random con? I have, it's not fun.
Another reason not to troll, consider the audience man! I know quite a few people who attend multiple cons over the year and seeing the EXACT SAME MOTHER FUCKING VIDEOS in the contest gets old REALLY quickly. You should be wanting to give the audience something new to get excited about or inspire them! Not showing them that as long as you know how to send to enough places you'll do well in life.
All of this can also lead to the question, why edit? While everyone has their own specific reasons, I've recently heard a few men at a panel I attended at AX say that their biggest motivator was that there were cons to enter and win. I never really thought people had that as their main mindset and it honestly made me want to vomit right there on the spot. Whatever your reasons for editing, if fame and fortune is your main and only goal then I think you're in for the wrong reason.
But then again, everything I just said is all personal opinion and based off of what I think is just plain ol' good morals
Now to answer your other question of which to enter, Masters or Expo...
How good is your video?
If it's something you really worked hard on and honestly have 100% faith in and believe it'll do well, I say Masters.
If it's something you made in an after noon with shit problems and a jumping aspect ratio of wide to full screen, fuckin' expo.
Masters is supposed to be the top contest while expo is "for everything else."
So yeah, those are my thoughts. No one here will change my mind.
Screw you guys, I'm outta here.
/takes off to go make dinner.