It really depends on what you like.
If you enjoy a relatively small community of intellig-
STOP THE WAR I LIKE BOTH I FIRST JOINED ROBLOX AND I LIKED AND BLOCKLAND I DON'T KNOW I LIKE AT 2 WEEKS AGO BUT I LIKE THE BOTH STOP IT FRICKING NOW!
intelligent people, then you'd probably like Blockland better.
If you don't mind a billion people running around screaming, many (if not most) of them being anywhere from six to eleven, then Roblox would be for you.
Is making your dream "character" a big part of the games you play? In Blockland, you make a cool avatar from the default parts (which is plenty in my opinion), maybe get a custom decal or two, and that's it. People may admire you for an original design, but it's definitely not a big theme.
However, in Roblox, you can easily find tons of custom faces and hats and shirts and things of all kinds, well made or not. And however good these may be, you must sometimes pay REAL money for it. So if you really have your heart set on that Spongebob shirt or whatever the hell Roblox kids would want, you're actually using money from the real world. Then, once you have this special custom design, people look up to you simply because you have, I don't know, a rare jester's hat. Rather than admiring (or hating) you for what your personality is.
What about add-ons? There's a big difference between the two games here. I can't really talk about making add-ons, because I have scripted in neither TorqueScript nor Lua, so I'll leave that out.
In Blockland, there's a much smaller range of add-ons to choose from. This is simply because there are not enough people willing to make add-ons (or not enough people willing to release their add-ons.) However, there's still enough things to get that can make your server fun and interesting, or just make the whole game easier (aka Duplicator.)
In Roblox, there's a TON of add-ons. You want an Iron-Man suit? Got it. A giant rolling pizza? Sure. A scorpion that shoots lasers which shoot ducks which shoot babies? No problem.
No matter how good they are, there's always something. This is probably the one aspect of Roblox that I like better.
And that's all for now folks.