Diminisher: looks very good... and it's good for Battlemaps because it does extremly Damage if you use its Ability.
Venom: it's very good for aliens, and for players wich have low Hitpoints.
Sentinel: It's very good if you fight against 3 people or more.
Spectrum: It's also a very good Design, if you fight against more than 2 Players. But the Ability only works for 30 Seconds Remember that.
Solace: It's very good in a group with 2 or 3 people who also have the Solace Design. Don't use its Ability if you dont have any Shield left 'cause 150.000 Hitpoints without shield, go down very fast.
I hope i helped you
p.s. I have every Design and i realy prefer : Spectrum, Sentinel and Diminisher.