I use both types.  Originally I wasn't keen on electric winch because of the lack of feedback (it would be VERY easy to rip the craft tow point out!) and the battery/outside installation.

For the Otter or smaller craft, electric probably isn't worth the hassle as its easy to pull these craft onto a trailer.  For the Explorer electric is probably essential (I used a 2-speed  manual winch for 7 years but it was very hard work)

I use this removable (hooks onto studs on the trailer winch post which means it isn't left exposed to the environment) winch type -  it is fairly low power (a good thing!) and relatively compact.  It has a manual override handle and a clutch (easy to pull out the cable).  It's powered from the vehicle battery so you'll need to extend the power cables to get to wherever the battery jump point is in yours).  The winch consumes 25A at full load so the vehicle battery can easily handle the drain from the winch (3 minutes loading time = 300W = 15Wh (full load - the craft will be less than half load) from a typical 80Ah battery of 960Wh ( in other words less than 1.5% of the battery capacity - you could load your craft many times without getting anywhere near to flattening the vehicle battery!

I use a remote control *winch has internal power relays so easy to add) and load from inside the craft so I can rock it sideways during loading to check for snags or other issues.

Downsides are:
1. Damage risk (leave the 'manual' winch handle attached so you can see the winch turning)
2,. Failure risk (the override handle is quite short and there is no ratchet so it would be hard work I suspect!).   
3. Slow'ish winch speed (6ft/minute)