When it comes to the 100mg/ml base, you should always be wearing gloves when handling it, no exceptions. It's a chemical and it is also a poison, especially in such high concentration. It's not dangerous if you take precaution. That being said, honestly, anything above 36mg/ml should be handled in the same exact way; with gloves.
PG/VG absorbs into the skin pretty quickly and with that, the nicotine. A drop or so isn't going to hurt you, but you should be cautious at all times because when it comes to a spill or perhaps the lid leaks (I've had it happen plenty of times), you're going to get more than a drop on you and unless you act quick and wash it off, it's going to soak in.
Treat it as you would any unknown chemical; prepare for the worst and keep kids and pets away from it, period. I wouldn't even mix my juice in the same room as either, just to prevent possible issues and I don't feel that's being overly cautious, it's just being smart.
As for concentration in general, 100mg/ml is going to result in less use and more PG/VG usage. Since PG/VG is the cheaper of the 3 primary ingredients, I always order 100mg/ml.