Best circuit to turn on a (5v heating pad) switch during the day?
I won't claim that this is the best circuit, but here is a circuit.

None of the transistors that you listed are up to the task. The MOSFETs have a marginally high Vgs thresholds. The BJTs have low max collector currents.

You want a circuit with hysteresis, without it, you may stress the transistor when you oscillate near the switching point. Adding hysteresis is easy with a comparator (LM339). 







simulate this circuit &ndash; Schematic created using CircuitLab

The threshold at the comparator is about 1.2V. The heater will activate when the LDR resistance is less than about 100k with the values shown.

Change R7 to change the light sensitivity. R5 adds hysteresis (small positive feedback). The MOSFET is a logic-level MOSFET. This one should be available in a hobbyist friendly package. 

C1 should be mounted close to the comparator. Don't forget to add decoupling caps near the comparator.

The comparator will draw a few milliamps. I don't know if that is low enough to be negligible for your battery. If not, there are lower power comparators. You could also increase R6 to 100k to save a little power also.