I've seen a lot of tetra grabbers I guess. There are a couple categories I guess and they depend a lot on how the tetra lifting mechanism works.
I'd say the best simple stab through design is probably swampthing's(179). To be honest is similar to my team's just a couple of prongs forward with a solid cross beam is all you need.
There are also the crane designs that grab the tetras through the top. team 38's had a great hold on the tetra and was an amazing design. The other great design i've seen is on good ole beatty(71). Their integration with their tetra grabber and storage area is very effective. I'd say that these designs are far from perfect in general though. THe tetras often sway quite a bit and are hard to place on the goals.
The final category is the dumpers. Most of these would stack up 2 to 4 tetras and dump them all at once on a shorter goal. I saw a couple good ones that did this, the gaelhawks(230), team 1402 and 381(i think...). 381 stood out because it overcame an issue with most of these tetra grabbers by really strongly securing them before dumping them. Something necessary when you become a goldmine of points and a target for all the opposing bots.
The most original and ambitious is probably wildstang's(111). Their double forklift side lifting design is quite amazing to watch in action(even on a crummy feed). It doesn't secure tetras tightly or provide an optimal method of delivery, but it is quite iimpressive in its ability to rapidly grab tetras.
A special mention goes to 865. A very very cool, methodic capping mechanism. It would store up a bunch over a long arm, and from what I could see on the feed, extend them up, unlock them, and flip them onto the goals. They had some issues, but defenitly the coolest! Not to metion it was paired with a swerve drive.
In general the succesful designs i've seen secure the tetra in some manner, either by clamping over it, pulling it in tight to their robot, or just gripping it in a manner that doesn't let the tetra bounce all over. The other key was being able to easily place them onto a goal. A team that easily places tetras onto goals is 121 the Rhode warriors. Their gripper keeps the tetras from moving around and locks the tetra in its orientation. The result is that they can rotate the tetra onto the goal. This defenitly eases teams abilities to cap tetras. The final key design was capping stored tetras seperatly. Not many teams can do this in a quick effective manner, but those that can like 71 are very succesful.
Looking back at this post i've defenitly spent way too much time watching FIRST robots in action
.