One thing to keep in mind is getting a blender well suited to whatever task you do the most. It mostly makes a difference in the style of blade and shape of the jar. Some brands will sell multiple styles that interface with one base, which might be the best way to go if you have the space for it.
The reason it's important is that blending a paste like peanut butter or mole is going to put a completely different demand on the system than turning tomato soup smooth, which is different that crushing ice. Some designs also work really well for large quantities, but not as well for smaller quantities.
I have an old Oster that kinda sucks, so I keep using it, and it will keep using it until it no longer works, and I can't fix it. If I were to buy one, it would be a vitamix 5200.
Personally, I dont like ninja (or the other half of their business, shark) cause their whole business is making knockoffs, which makes me suspect of their quality. Their blenders seem to often have the giant stack of blades, which is good for shredding up a smoothie, but it's not well suited to some other tasks.
Personally, I like SeriousEats for reviews and comparisons of kitchen implements.