I don't use Spark because if you have push notifications turned on (and who wouldn't?), Spark stores both your email credentials and your messages on their servers. No thanks. Gmail is my primary email, so I use Google's InBox app, but still keep the stock mail app set up (without notifications) because I find it easier to compose longer messages, and reply to specific messages within a thread of messages, with the stock mail app.
I'm not quite sure I understand why you'd actually uninstall any stock apps. I just put them in a folder in a home screen far to the right and just ignore the ones I never use.