You do, however want to consider your flash setup and what you are using it for when making your choice(s). Is this for a studio based strobe setup or Speedlight setup, small product shots, full length portrait work, group shots, outside work etc etc. Flash power will have a bearing on what modifiers you can successfully utilise. Umbrellas should be considered (in my opinion) in the same way as softboxes really, the bigger they are the larger the spread of light and the more the light wraps around the subject. Larger modifiers require more power of flash generally.
If you only have a limited power system/Speedlights you may find that the diffusion properties of a shoot through umbrella with a silver/black outer cover does not give you the results you were expecting from say a silver reflective umbrella.
So, you need to consider what you want from your modifiers, and purchase your type and size accordingly.
For example I use only a Speedlight and often for close portrait work outside, so I have 36" silver reflective umbrella and some simple reflectors as it fits what I want to do with it/them. If you want softer then go for a white reflective or shoot through or softbox.
Does that help :shrug: