Unfortunately this is not a question that Wonkee can answer easily, as it depends on the nail puller you are using and its specifications. It will also depend on the style and condition of the nail itself, as well as the material you are removing the nail from.
Some traditional nail pullers have jaws which only need to grip the shaft of a nail.This grip will tighten as the tool is pivoted over,so that it can be repositioned to pull a longer nail out a bit at a time by placing the jaws around the part of the nail shaft which is closest to the wood.
Other traditional nails pullers will need to use the head of the nail to grip under, it will depend on the specifications of the individual nail puller.
Usually the nail pullers with handles are designed to pull larger nails are they are larger tools and built for tougher jobs.
The advantage of a traditional nail puller is that it can reach under timber to pull out sunken nails.Once the nail head has been exposed, another nail pulling tool can be used if necessary.
The longer the tool, the more leverage it will be able to apply to removing nails.
Heavy duty nails will probably require a heavy duty nail puller such as a large crow bar or prying bar.
It is worth noting that ring shanked nails or square twisted nails, with twisted or ringed shanks, will be more difficult to remove than standard nails, as they are designed to be a more permanent fixture.
Coated nails have a coating of adhesive on their shank, which is melted by the friction from the nail being hit into the material, this adhesive then sets to hold the nail firmly.These types of nails will also be more difficult to remove.
Also, thinner more delicate nails and brads may be broken or snapped off by the sharp jaws of the nails puller.