I've used the shellstrike many times as a secondary in double HP wars, really effective and fun to play with.
The trilogy feels realistic honestly, and has a fast reload time. Super fun to use as a slung secondary, but not very good as a primary.
The Gjallhorn is just too big. Fun to plink with but not suitable for nerf wars.
The sledgefire has a decently fast reload time for me. But I hate the blaster design and the reload system. It's not as fun as the other 3.