Some pros and cons from Mexico. We have been doing 4-5 long line rescues per month for several years now in some of the roughest mountains on the planet so we have some experience.
Long line pros
Expense and don't tell me price is not a consideration. If that were the case we would all be using Boeing 234's or Mil 26's complete with doctors, nurses and an ER on board for rescue work.
Long line is a simpler system. No electrics, gears, brakes, cutters, guides, operator etc. The cargo hook electrics are disabled during these operations.
The ability to put multiple rescuers and/or victims on the line at the same time. The usual is 3 medics and one litter victim at a time. We have only put a single rescuer out once. We feel that a single rescuer is a marginal situation for the evaluation, preparation and loading of the victim. The victims are fully enclosed in a cover to isolate them from the environment.
We have a basket that will handle up to 15 people at a time that we are experimenting with but have not used yet.
We have never had a victim/rescuer spin as I have seen during hoist rescues. The video of the LA county paramedic and victim is sobering.
The pilot has an unobstructed view and complete control of the load, no need for third party instructions and confusion. Presision placement of the rescue personnel without the need for "Tag Lines" or any other assistance from the ground.
In the time it takes to winch a victim 100 ft and load we can usually have the victim to a suitable landing area where he is loaded internally.
In the US, hoist operations are a Part 133 Class "D" operations while long line operations are Class "B". There is only one approved EMS Class "D" that I am aware of. That approval is hard to get to say the least.
Cons
If you have an engine or tail rotor failure during external load operations it really doesn't make any difference if it is a hoist or long line. You either have fly-away power and/or control or you don't. But then how many of us are flying transport category helicopters with true single engine performance at normal operating weights and altitudes? The ending is going to be very similar.
The requirements on the pilot are much greater. But to a good logging/seismic pilot/long line pilot it's "just another load" and a light one at that.
Fire away.