Originally Posted by MRT2

It isn't so much the number of speeds, but the gearing range (particularly the lower range) you need to pay attention to. These days, you can get 3 x 8, 3 x 9, and 3 x 10. Or you can get a compact double, usually either 2 x 9 or 2 x 10 (or even 2 x 11).

You need to get a bike with the useful gearing for your weight. My current bike has a relatively close ratio 12 - 25 tooth cassette, but a relatively relaxed 48 - 36 - 26 triple chainring, so the lower chainring offers a range of useful gearing. Whatever bike you get, make sure it either has a cassette with a large bailout gear (at least 28 tooth, preferably 32 or 34 tooth), or a small chainring with 26 teeth or fewer, or both. A lot of roadbikes from the 70s and 80s, even current ones have gearing not suited for bigger riders, like a 52 - 42 crankset, with a close range cassette or freewheel.