I think JW's were a cult in the beginning seeing as how they were founded by a man and were too new to be accepted by the general population as a full on religion. Those who have a complaint against JW's tend to use the term cult because it has a negative connotation in our society and using that word is sort of an intellectual way to engage in name calling.
As far as I can see, there is no specific line of demarcation between a religion and a cult. To me, JW's are a religion with cult like overtones. When it comes down to it, I suppose Jesus was viewed by some as a Cult Leader at one point and Christians were his Cult. Most religions were probably cults at one time until their warped views eventually became more mainstream. They all have a degree of hold over their members and strive to ensure that they all hold the same beliefs and are moving in the same direction.
People who feel left out or misunderstood by the general population for some reason, tend to be attracted to unpopular or off beat religions like JW's. Like anyone else, they are on some level, looking for answers to unanswerable questions but they don't fit into the already existing religions. They feel extra virtuous by being part of something that is looked upon as odd or a bit crazy by others. I know some JW's who would be utterly disappointed if JW's were ever thought of anything but offbeat and they very much dislike the recent changes that make their once quirky religion, more mainstream.
JW's raise their children in the religion and the children often feel alienated from the general population like their parents did, but unlike their parents, it's because of the religion itself. The parents as well as the children are caught up in the religion because of it's cult like aspects. Most if not all of these cult like aspects come from the man made rules and policies rather than from the actual doctrines themselves. There is limited information about the inner workings of the organization and there is a price to be paid if one leaves.
Anyway....rambling thoughts but that's my take on JW's. If I had to choose just one of the terms offered to describe JW's I'd have to go with "High Control Group".