At the beginning of TNG the Type-II Hand Phasers were made on the larger side, starting with the Dustbuster Phaser (predecessor to the Cobrahead). It didn't take long for them to redesign the Type-II into the more familiar Cobrahead Phaser we saw throughout the rest of the series.
As for that variant of the Type-II, it went through three different alterations. The first version was large like the Dustbuster Phaser, had more rounded edges and featured a light-up PLI (Power Level Indicator). The second version to come out was a little smaller, was more angular and had sharper edges and sometimes featured a PLI and other times didn't.
The third and final version seen closer to the end of the series was the smallest of the Cobrahead design, had sharp edges and never featured a PLI. Oh, and if I remember correctly, the first version of the Cobrahead had the top ribbed grip reversed from what we normally see.
Someone posted a great comparison pic of the three versions somewhere else (maybe TPZ?), if they're a member here hopefully they'll post it for us to see.