Stella is a warrior with brute force but thinks on her feet. Raised in a military base with a hardheaded Chrome, an honorary veteran general Bronze, and a walking tank by the name of Iron. She's a blood knight who'd fight to the death if she has to.
Spark's was raised by a group of criminals and mercenaries who do dangerous work but would always do it out of necessity and survival, her adopted dad is literally a Trap. She'd be a stealthy tech expert and plans ahead before rushing into dangerous situations. She'd read the enemy and have 1000 different plans to kill them before even confronting them. Her weaknesses are direct confrontation and deviating from the plan, but by then she'd already plan a dozen escape routes. If that fails, the enemy would be so low on equipment by the time they catch up to her and she'd just snipe them at her tactical position.
Her lack of strength is her strength. A thief with a heart of gold and it would fit her name as Sparky- she works with technology. Doesn't mean she's not dangerous when confronting her, she probably has an arsenal up her sleeve, as she's hiding behind a series of bombs and traps.