1. A neckline beard helps cover up your double chin, if that is a problem for you. A jawline beard on the other hand, highlights your double chin.
2. When you start growing a beast beard, you cannot keep your neck clean shaven and it will be very difficult to suddenly grow hair around your neck. So, it’s important to not shave your neck when you are in early stages of your beard, even if a designer stubble stage. A jawline beard yet again stands as a negative here.
3. A jawline beard is easier to achieve as compared to a neckline as you have the perfect edges to trim around i.e. your jawline. However, because of the very same reason, it lacks challenge. Also, it is a bit more common. If you wish to look out of the box, you should opt for a neckline trim.
All in all, neckline trim wins. It may be difficult at first, but you will be able to master this trim as any other and it is totally worth it.