While many modelers solder joints and power connections, none of the brands of track sold today require soldering, so don't let that influence your decision too much. The most common choices are Atlas, GarGraves with Ross switches, and Lionel FasTrack, but there are layouts done using all brands.
GarGraves is one of the most popular due to price and availability. Ross switches are arguably considered the best with the most options and many modelers use them regardless of what brand track they buy. Atlas is arguably the quietest track and easy to keep clean, but I've seen GarGraves layouts that are also very quiet. Because of the plastic roadbed, FasTrack is the least quiet of the 3, but there are things you can do to lessen the noise. ScaleTrax is arguably the most realistic looking, but curve sizes and switch options are limited, especially for those modeling in small spaces, and availability can be problematic. ScaleTrax FlexTrack is by far the easiest to bend, though people have had good success bending GarGraves flex.
The biggest reasons many modelers choose a particular brand are the sectional curve and switch sizes that are available for that brand.
Atlas has O27, O36, O45, O54, O63, O72 and so on.
GarGraves has O32, O42, O54, O63, O72 and so on.
FasTrack has O31, O36, O48, O60, O72 and so on.
Atlas and FasTrack offer straights in various small increments from 1 1/4" to 10" and then long pieces that are 30" or 40". Here GarGraves is the odd ball in that their smallest piece is 6.2" followed by 12.4", 24.8" and 37". However, GarGraves is arguably one of the easier tracks to cut to size and many modelers don't like using the small filler pieces offered by Atlas and FasTrack. That is also where soldering comes in to make joints stronger and more seamless. The number of (unsoldered) joints can affect power and command control signal transmission. Most modelers add power drops every 10' or so and of course, soldered connections are better than pins and joiners that are prone to loosening over time.
And then there's cost. Atlas is the most expensive and while you can find discounts online, you'll often find bigger discounts on the others. That said, there are plenty of modelers who are happy with every brand of track.