There are fans of the 1100 and fans of the 11-87 ...and shooters that like semi-auto shotguns that like neither of them....same in all things !
"Better" is relative....but in terms of reliabilty and durability both are about the same. There are some differences in chamber length on some models / and you should probably focus on what you want to do with the gun / what chamber length you want or need vs which model.
Both the 1100's and the 11-87's have killed more game birds in the field - than any of us could ever count.... I see them both models on clay target fields all over the country.../ in a variety of gagues.
There are a lot of gas operated shotguns out there these days....Beretta probably has 35 different models / Browning-Winchester have several models --- etc....
I think in general, its fair to say that Beretta is making some very good guns these days ..in a variety of configurations. I like Browning - Wincheste a lot ..especially the Browning Silver series for an entry level gun - and its on sale in some of the "big box" stores right now for Xmas...
but the 1100 is not better than the 11-87 or vice versa - in my opinion.