Soft play
Usually the cheapest per head, generally somewhere around £100 to £250, and very hard to beat for children under six who mostly want to run about. You travel to the venue, the venue does the food, and you are out in two hours. The downside is that it looks and feels the same as the last four parties everyone has been to.
An entertainer
A magician, a science party or a disco. Good for mixed groups of boys and girls, strongest for ages four to seven, and it works in a hall or at home. The entertainer holds the room for an hour or so, which is either exactly what you need or slightly less than the whole party.
A pamper party
Works from about five upwards, and keeps working right through to twelve, which most party formats do not. It is a two hour experience rather than an hour of entertainment, it happens at home so there is no venue to hire or travel to, and the children come away having made something and worn something.
It suits a girl who likes the idea of being fussed over with her friends. It does not suit a child who would rather be upside down on a climbing frame, and we would say so if you asked us.
Cost, fairly compared
Look at the total, not the headline. A venue party often adds food, party bags and a deposit on top. A mobile pamper party at £250 to £425 includes the robes, the activities, the gift bags on some packages, the travel, and the tidying up, and you are not paying for a room.
The honest answer
If your daughter is four and full of beans, book soft play. If she is seven and has been talking about a spa day since Christmas, book the pamper party. We would rather you enjoyed the right party than booked the wrong one from us.