I have had a number of different ones and I would say it depends what you want to do. For example, I lived in temporary accommodation for a few months when we first came over to Switzerland and so all my kitchen wizardry had to be in storage. So, I wanted a machine that did everything I.e. Liquidised soups, made burgers, did breadcrumbs, made smoothies, chopped veg etc. but now I have all my other equipment back I want it to basically prep stuff. I have the one with the two containers with lids and find that excellent. I use it virtually very day and that is the one that I would replace immediately if it broke. I like it best because the two containers can be rotated through the dishwasher and you can prep food ready to cook quickly when the children get in from school. Also, the bigger one that I had (I think it may be 700w) was just too big and too powerful for doing the prep jobs. It was difficult to control if you just want to cut one onion and then you had to put it in a different container to store in the fridge to cook later. The one with two containers is easy to pulse and control. And the containers on mine fit in the fridge shelves (I would measure and check these ones fit in your main fridge shelves). I use mine for:
Chopping onions
Chopping carrots and celery
Chopping garlic and ginger (stir fry)
Grating cheese inc Parmesan
if you want to make more smoothies and liquidise soups then you would want to make sure you had the bigger beaker. Mine just has the two smaller beakers with flip lids which is fine as I have got liquidisers for that!