I previously used MFP and will be using it again after baby. You can change your calorie allowance and the macro breakdown. I used a site called iifym to work out what my carbs, fats and proteins should be based on my goals and weight, then just changed the macro breakdown on MFP to those
I don't know anything about the weightwatchers app, but I use mfp which is simple to use and I can usually find the info for food I am eating or a good approximation. Draw backs are it tends to suggest everyone eats 1200 cals a day no matter what their starting weight is. Not all the nutritional info is available for every thing, so if you want to monitor say iron intake the figures are not very reliable. I just use it to log basic calories and ignore it's prompts about protein/carbs and so on. For that it works well.