I'm thinking Broken Steel since it continues with the main story.

do broken steal 

Broken Steel to raise the level cap, then Point Lookout.

Broken Steel!

I know which one shouldn't buy, and that would be Operation Suckage.

Alright, Broken Steel and is it correct that Operation Anchorage isn't worth it? Or should I get it also?

Operation Anchorage is kinda lame, alot of shooting not that much story (I don't think you can make a single choice in the entire DLC) doesn't add much to the overall experience of the game.
All of the other DLC is much much better.

Broken Steel is necessary. Period. THEN,

Point Lookout>The Pitt>Operation Anchorage

Operation anchorage gives you access to some of the best stealth items in the game as well as some of the best most useful weapons.

Operation Anchorage gives u Gauss Rifle and stealth armor. not much to do there after u are done tho. i would stick with Broken Steel if i were u

also anchorage gives you early access to power armour
and its armour that never needs repairing

plus the story to fighting in alaska is fun and interesting imo

" Alright, Broken Steel and is it correct that Operation Anchorage isn't worth it? Or should I get it also? "

Been playing Point lookout for a few hours now and it makes a nice change of scenery. Broken Steel fixed a lot of what was wrong with Fallout 3 and although the quests were some of the best in the entire game, it was a bit short I felt.

From what I can tell, Broken Steel for the level cap than whatever you fancy afterwards.