They're different but there is some overlap in the characteristics they share:
The soyboy (aka the "nu-male") usually falls under the characteristics:
- "Manchild"-like interests, including video games (specifically Nintendo and the occasional pretentious indie game), Marvel movies, and Star Wars
- Bald or balding, hipster glasses, beard whether they can grow one or not
- Usually with mouth open in photos
- White-knights women constantly and nods along with their political beliefs (almost always liberal)
- Tends to drink soy-based beverages and trendy foods (hence the name)
- Often fetishizes urban environments (but only the nicest, upscale stuff)
Modern neckbeards are more nebulous these days, but often fall under the same characteristics:
- Almost always white
- Overweight and poor hygiene
- Fairly strong political beliefs but underdeveloped, various flavors across political system
- Either "misogynist" or full m'lady, no in between
- Video games in general
- Anime (may have waifu)
- No friends or social life