I'm speaking as someone who has lived with both and only just fitted a non-outside filtered one that purely relies on the charcoal filters.
Ideally you will want an outside filtered one because that is what works best. However a lot relies on the layout of your kitchen and where the hood will be in relation to an outside wall. My current kitchen is open plan and very well ventilated already due to space and window positioning. I declined an outside vent due to the mess and unsightliness of the vent run.
You will need to consider the size of your kitchen, natural ventilation, how many times you're likely to cook sprouts, broccoli, smoked haddock and as ColinJ says, the noise of the thing when it's running.
I've got an Indesit one which works fine if a touch noisy.
Are you ordering through a kitchen supplier or buying yourself? I ordered through Argos but they let me down the day before delivery despite a 6 week order time. Ended up doing what I should have done in the first place and bought from John Lewis. 48 hours from order placed to delivery with the two year guarantee.
One last thing, stainless steel looks nice but is a b**ch to keep clean.
