A submersible pump with a vertical sliding switch, not the flop around float type or the trapped air micro switch.
The flop around jobs can easily hang up, and any debris can clog the tiny (1/8 inch) hole used for the membrane micro-switch type.
Be sure to keep a lid on the pit. At 8 feet it should be deep enough to avoid freezing if covered.
A union that you can reach from the top allows you to disconnect the drain line and use the pipe to lift the pump out if needed.
Watch out for trapping water above a check valve and having it freeze.

Very good point about the float type switch. A neighbor of mine got water in his basement because his float got hung-up on some trash in the pit, causing his pump not to activate. This was a new construction, so I imagine some trash had accumulated in the pit from the building process.
Anyway, be sure to check your pit occassionally for any trash or debris.