If you are running an FA sniper build, depending on whether you want to run 1 or 2 snipers (it sounded like 2), then you really need 2 other types of weapons:
Something that works both up-close and personal and at mid-range; and
Something to help cycle FA.
For 1, I would say that the Light Show, Flipper, Robin’s Call, Clairvoyance, Monarch, or Hellshock all would be great choices. I feel certain I am missing some really good ones too.
For 2, your only real choice there is the Reflux, or if you can’t get one of those for some reason, the Brainstormer (Redistributor can work in dense mobbing too, but if you can get a Reflux or a Brainstormer, I don’t know why you would go with the one that is hardest to farm LOL).
In my sniping builds, I usually run one “feature sniper,” typically the WI or UT, and then a Recursion, Monarch, and pistol in the 4th slot (Maggie, Light Show, and Seventh Sense all would be good choices for an FA build, or you could rock a Hydrafrost too, I really like that one).
A lot of your secondary weapon choices in a sniper build will depend on your COM passives as well.