There is no simple one line answer, because every "stand" is different.
Neither one is a magic pill, as calling is only one component of successful predator hunting. Electronics are not legal in Alberta, but I hunt in several places where they are. I sell both hand calls and Foxpro electronics, so I have access that most hunters don't. I also guide/call about 120 days a year for all predators. I'm not bragging, but rather qualifying what I say.
I really like hand calls, because they give me better control of the predator as he comes in. I can get aggressive on the call or I can squeak, whine, moan or whatever it takes to keep the predator interested and coming in. With open reed hand calls. I can howl, yelp, whine, or make a large variety of distress sounds, and I can do this immediately. The downside is the target is focused on me/sound. I have to remain still and, while some may not agree, be camoed. The other problem that we have in Canada is with closed reeds freezing in the winter. They are much easier to learn to use, but they lack the versatility of an open reed. The open reeds don't freeze.
With electronics, there are several products on the market. I would go with ones that have no moving parts, a remote control, no sound cards, and the ability to load sounds from other sources.
The advantage of electronics is the sounds are very good, and loud, even when the hunter is not.

The remote control allows the caller to be placed away from the shooter, so that when the predator comes in downwind, he is focused on the caller. While you can change sounds and volume "on the fly" with the better callers, it is not as fast as with a handcall. It is very effective, just different.
There are so many things that go into a successful stand, setup, wind, sun, approach etc, etc.. The hunter must try to cover as many aspects as he can. Electronics shorten the curve.