Netherland Dwarfs have a reputation for being nasty. They seem to have improved recently though - my bucks are very friendly albeit flightly. My does are still kind of mean. Lionheads, from my experience tend to be a bit friendlier than netherland dwarfs - most lionhead does Ive met would tolerate a lot more than what a dwarf doe would, and the bucks seem a bit less energetic.
Netherland dwarf adults themselves dont have too many health issues - but it seems they have a monopoly on birth defects - peanuts, hippos, max factors, faders - if you breed two show quality netherland dwarfs together, expect at least a quarter a babies to die within the first week even with a perfect mother. Some lines also have difficulties with birth due to the large heads, but good quality lines generally dont have that problem because of the wide hips. Lionheads generally have larger, healthier litters. Not to say lionheads don't have any problems - some lines of lionheads have been bred into ND and have similar problems, but as a whole lionheads tend to have less problems. Also, lionheads can have some problems due to the mane - you need to take care of their wool.
Netherland dwarfs are expensive little rabbits. Most of the ones I bought cost around $150. Even higher quality ones go for even more. Netherland dwarfs are so particular and have such small litters, that they have a low supply of good rabbits and a high demand for them, so the prices are high. Lionheads are much more variable. Both are hard to find good rabbits - there are a lot of pet quality lionheads out there that have been bred into show lines, and as a new breed there are some different interpretations of the standard (and some lines were bred to fit the older standards), so you have to be careful when buying. These are two very different breeds - I'd suggest getting a couple of each, and getting to know the local breeders of each (lionhead and dwarf breeders in general are very different groups)