depends what your after.
SC2 is an army level game and playing a single player grand campaign game from start to finish takes about 10+ hours. This doesnt have to much replayability i.e. you can only be axis or allies and replaying as either one a second time will be pretty much the same game experience.
There will be quite a few mods out for it though, and this will extend the time you play it.
This changes on player vs player where the game truly shines, you will find no 2 games the same and its a reasonably stable way to play.
The game is simple to learn how to use, one of those beer and pretzel games. Game with latest patch seems reasonably bug free - no crashes etc. Downside is comp AI is appalling, but this will be fixed in forthcoming patches. Perfect for a few hours of gaming against a friend.
HOI2 is a division level game (although I tend to play it with divisions grouped as corps). It will take you 100+ hours to finish the single grand campaign. This does have a lot of replability as you occasionally get some very ahistorical occurances, and playing as each country (and theres a lot of them!) tends to be a different experience. There are also some excellent mods out there for it, such as stony road to war, total realism project and community open resource exchange project (eventually). Your looking at over a thousand hours of gaming here, thats a lot of time for its price. There is also an expansion pack out for it so its a 1936-1953 game.
Player vs player can be a great game, they seem to have resolved the issues with that. However this isnt a 2-3 evenings experience, you really need a fair bit of free time to do player vs player.
With latest patch + one of the mods or the expansion pack the AI is challenging for the average player and not to bad for an experienced one, altough this will improve over time.
It is very stable and reasonably bug free.
It is more complex to leran than SC2 because of its greater depth, but I found both games trivial to pick up and play unlike War in the Pacific.
The amount of micro management is up to you, as almost everything can be left to computer advisors and they do a good job. (at least with the expansion pack)
Both games allow you to mod the game, and if your into modding thats a real plus.
So in short you get far more value for money with HOI2, but that requires greater time investment so really depends on how much free time you have to play games