Like the 'what is a hybrid?' question, there is no definitive answer. It depends entirely on a few important factors.
What are you intending to use the 'hybrid' for?
What weather conditions are you going to use it in?
How fit are you?
If you live somewhere flat (Norfolk is as flat as a mill pond if I remember correctly?) and only intend bobbing around the local area and to/from work etc then you hardly need a mega range of MTB gears set-up. In this case I would suggest a single or double front chainset with a medium range rear gear cluster, 12-26 or 12-28 where 12 is the teeth on the smallest gear and 26/28 is the teeth on the biggest. I would also suggest considering one of the shimano rear hub gear sytems as these appear to be quite good now and are simple to use and maintain. On the other hand, if you think you will be heading somewhere hilly, or carrying a lot of gear, or feel particularly unfit then you might want to choose those MTB gears with triple chainring at the front so you have the easier gears needed to crawl up the inclines
If you might be commuting in attrocious weather a lot then simplicity and reliability are important. This again might push you towards a geared rear hub as they are protected from the elements but my GT hybrid has derailur gears and in 18 months of all weather use has had hardly any attention at all so they are not the evil some make them out to be. The simplest gears of all are no gears and if you are using the bike somewhere flat for shorter journeys (3-4 miles) then consider a single speed bike. This is not to be confused with a fixed gear bike! A single speed bike still has a freewheel so you can stop pedaling when ever you want. You might need to mess around swapping the single rear cog until you get a gear you are happy with but for a flat area and utter simplicity this is a great solution and also makes for a light bike with uncluttered handlebars (only brake levers needed).
The question of fitness is something only you can know. If you are just starting out and are really worried about struggling then the triple chain ring will give you the most gearing options and there will be a gear for every situation but you might find that after a while you just won't need to use many of the easier combinations and may never even drop onto the smallest chainring at the front. If you are an experienced cyclist or are relatively fit then you could skip the triple set-up altogether and just make do with the medium range gear cluster (cassette) like the 12-28 mentioned above. If you are really confident in your ability and live in a flattish area then you could go to something like an 11or12 - 23or25 cassette which will give gearing similar to a sporty roadbike.
As I said at the start at the start, there is no definitive answer and maybe that is the beauty of the hybrid bicycle. You are free to pick and choose elements from the various cycle disciplines to create a bike that is flexible and useful to your needs, not one that is trying to conform to the expected norms.