Every year around this time I see the same incorrect phrases pop up.
"Samhain is the pagan new year."
"Samhain is the witches' new year."
No. No it's not. A new year for some pagans, witches, and Wiccans? You bet. The new year for all pagans and witches? Not even close.
Both paganism and witchcraft are hugely diverse groups, and that includes holidays. The Wheel of the Year is not universal among all pagans and witches. Not all pagans/witches even celebrate Samhain, let alone consider it the new year. Some follow totally different holidays. For example, many Kemetic (Egyptian) pagans celebrate their new year - Wep Ronpet - with the rising of the star Sirius, currently around the beginning of August.
For those that do celebrate the Wheel? The new year doesn't always fall at Samhain. Many choose to celebrate the New Year with the rebirth of the sun at Yule. I have also met several pagans who prefer to place the new year at Imbolc, or even Ostara. This can be true of Wicca, as well. Many Wiccans do celebrate the new year at Samhain, but many celebrate at Yule as well.
Some argue that since Samhain was the Celtic new year, it's wrong to do it differently. That doesn't really make sense for two reasons, though. The Wheel also includes Yule, which was the Germanic new year. More importantly, the Wheel isn't a reconstruction of any one culture. It's a mash up of different holidays and traditions. Given that, is it really so strange we sometimes celebrate in different ways?