It's not just the aperture you need to look at. OK a f 3.5 lens lets in a bit more light, 1/3 stop to be exact, but it's the lens itself that controls the overall quality of the image. Therefor a lens with an aperture of f4 may give better image than a f3.5 one
I'm not over keen on lenses with a wide zoom range. It's a lot to ask from the optics to give an 11x magnification at an affordable price and maintain image quality. However it's up to you to judge what lenses are best for you.
The other aspect is converters. I have the Canon 1.4, but use it infrequently. I thought about the 2x but there is some feeling that the 1.4 image cropped gives a better image than the 2x at full frame.
What is your budget? Also what camera are you using? Finally do you really need a zoom, could a prime lens do the trick for you? These can be cheaper and often give better image quality.