@ Imist there are many types of speculums . However I suspect that you will be more familiar with both the Graves and Pederson Vaginal speculums as these are the two most commonly used speculum used in the US. Although some Doctors/NP also use the Cusco Vaginal Speculum. In the UK they tradionally use the Collins and Graves vaginal speculums .
Links to the various type of speculums:
Graves
http://medgyn.com/wp-content/gallery/instruments/GravesSpeculum.png
Pederson
http://medgyn.com/wp-content/gallery/instruments/pederson.png
Cusco
http://medgyn.com/wp-content/gallery/instruments/cusco.png
Collins
http://medgyn.com/wp-content/gallery/instruments/collin.png
I think in addition to the type of speculum you want , you also need to think about the material the speculum is made from either metal or plastic. Both has their advantages and disadvantages , but in all honesty It's down to individual preferences . Some women like the cold feeling of the metal speculums while others dont. So say the plastic pinches while other don't , and the clicking of the plastic speculum can be a bit disconcerting. Whatever you choose good lube is essential when using the speculum as well as good and effective cleaning.
Speculums ranges in sizes and lengths from virginal to extra large and as you go up in size you get the ability to open the vagina more . How wide you can open depends on how comfortable you feel , some women regardless of having children or not can accommodate a large speculum open to its maximum , while other tend to only accommodate a small. I think it all depends on how relaxed you are , if you tense up then the insertion of a speculum can be uncomfortable and painful.
Traditionally the Graves, Pederson and Cusco open vertically , while the Collin's horizontally , but all can be used either vertically or horizontally , though those with handles like the Graves, Pederson and Cusco can be more awkward to use horizontally.
There are speculums that can open both vertically and horizontally like the Four-Way Vaginal Expanders although I have never seen them in use. The Four-Way Expanders provides 50% more lateral working space at the introitus ( vaginal entrance) than a standard Graves speculum.
http://www.utahmed.com/images/fourwayexpander(large).jpg
As for a bit intimidating I like the look of the Trelat speculum , the blades can be opened on a runner to approx. 55 millimetres with the upper cog wheel. An extreme stretch of up to 15 centimetres can be achieved with the lower adjustment screw.
https://upload.wikimedia.org/wikipedia/commons/5/50/Spekulum-Trelat.jpg
With regards to the companies , I'm sure if you google the medical suppliers near you , you will be able to find them . As a general rule the better quality speculums cost a bit more .
Hope this helps
RN