For years I refused to spend money on a food processor. What a shame. I now have a full sized, a miniature, and a “chopper” – a hand operated version. The “chopper” was my first. I used it for making guacamole and salsa. I loaned that out and did not get it back soon enough and got desperate for an aid in making my salsa. So, I purchased a mini food processor. The mini works great for your everyday stuff like cutting up a little garlic or onion. With onion it helps to minimize crying! Later I was making salsa weekly for a local restaurant and gave in and bought a full sized food processor. Now, I use all three and have found that they each serve a unique purpose.
If you are willing to donate the elbow grease, the chopper is best for guacamole and salsa because the motorized types can cause a foamy effect, particularly with guacamole. If you can only purchase one I recommend the mini food processor. This is purely personal choice, but when you are just working with small amounts, such as garlic for one meal, the full size just throws it around, and most of it is stuck to the sides. If you make a lot of creamed soups, you will want the full sized. You may still have to work in batches, but it will go much faster.
The reason I recommend food processors so highly is really convenience/quality. The food processor saves so much time and effort that you are more likely to use fresh ingredients, and therefore produce higher quality meals. If I did not use the food processor, I would get lazy and use powders more often than fresh.
Then, there are salads, etc, which can be made without cutting all those ingredients by hand, if you just slide them through the food processor. Once you establish the habit of using a food processor, you will naturally revert to using fresh ingredients. You and those you cook for will notice a huge difference!