I understand the Ninja is bigger and has more power, but I can only speak on behalf of the Nutribullet (since I own one). I use mine at least once a day, and often twice a day. It totally annihilates cashews, walnuts, and ice with no problems. Its size is perfect for me too. There's just me, so I have no need for a large pitcher serving. Also, the Nutribullet comes with a recipe book and diet plan, if you're into that.
Before I had my Nutribullet I had a Ninja and it broke!!! It could not take the ice chopping every morning... did not last long... so far my Nutribullet has been great chops everything in a matter of seconds... I love it...
Can't speak about the Ninja as I don't have one. However, I have 3 juicers and 2 blenders. I hate to drag them out unless I'm going to make lots of juice or pulp because it's humbug to clean up. I like the Nutriblast because it takes little space on the counter, works very well, makes just the amount I will use at each serving, and the clean up is a snap. Because it works so well for me I use it very often. That is what counts for me.
I bought the Ninja Master Prep Professional QB1004 for $59 on Amazon. It was tied for HIGHEST rating with the consumer reporting source I use. So far, so good. The other top rated blender was the Vitamix at $450. Ouch! Then the Ninja NJ600 in the $100 range. No brainer for me.
I don't know anything about the Ninja; but I've been urged by some of my friends to either get my money back from the makers of Nutribullet or get them to replace it. I have to admit, when the Nutribullet worked, it worked really well. I was using it pretty much every day making breakfast smoothies and/or green smoothies for the afternoon. I was really bummed when it died. Sorry I can't help you any more.
between those two go with the Ninja. Customer service for Nutribullet is almost non existant. If you dont believe me call them and go throught he phone tree go for the repair/warranty option and see what happens.
I haven't used the Ninja NJ600 so I cant tell you how it preforms. Is a blender and I guess you could use it to blend your vegetables and fruits. I find that the Nutribullet is easier and quicker to clean than any blender or juicer I have used in the past. It will also pulverized the fruits and veggies into a nice smoothie. I dont lnow if the Ninja NJ600 will do the same. I guess it depends on what your preference is. I hope this was helpful.