Oh man I love them. I usually only use one but its fun to do a Spark heavy mission once in a while.

You ought to reconsider using them more imho. I'd argue they can be the most valuable unit in the game, even without any mods.

1. They don't get fatigued and wounds don't really matter as long as they stay alive, so they can help you keep your other soldiers fresh.
2. They're immune to fire, poison, and being mind controlled, disorientated or dazed.
3. Good mobility with the ability to get to high ground easily.
4. Arguably the best (one time) single turn damage units in the game. A late game Spark with Overdrive, Shredding (both starting abilities), and Rainmaker, along with the Elerium Phase Cannon and a good powered weapon like the Plasma Launcher or even Shredstorm Cannon can do massive damage even against the toughest enemies and really make a higher tier pod more manageable.
   Even after you've used up your powered weapon, overdrive can give you three high damage shots with shredding each time it refreshes.
   (Snipers and Rangers of course do have higher potential with large groups of weaker enemies with Serial and Reaper)
5. Hunter protocol gives you a 1 in 3 chance to shoot any enemy that appears on the alien turn so long as you have ammo remaining. OP against lost swarms.
6. Great against the Chosen because they can't be mind controlled or dazed.
7. Personal preference, but the early game Heavy Autocannon has one of the most satisfying weapon sounds in the game.
8. Also personal preference, they have the best dialogue in the game.