Did you happen to read the stickied thread at the top of this forum titled "Buying your first scanner? Read me first!" http://www.railroad.net/forums/viewtopi ... 43&t=15906
There's also another stickied thread at the top of this forum titled "Scanners-What do you use when railfanning?" that will give you an idea of what other Railroad.Net forum members are using.
To briefly answer your questions (not in order):
What brand is the best?
A subjective question-Everyone has their own opinion. Your best bet is to read
and make up your own mind which scanner will work best for your purposes. Are you going to be monitoring other activities (local police, fire, EMS, marine band, aircraft, amateur radio frequencies) or are you strictly interested in railroad radio?
Whats a bank?
Short for memory bank. My first handheld scanner, now 25 years old, held 10 frequencies-period. Newer scanners can store hundreds (some thousands) of frequencies. Scanning through all of these frequencies can take some time. If you specifically want to listen to a particular activity you can "lock out" certain banks and focus on the activity you're interested in.
How many frequencies can it hold?
As mentioned above, different scanners have different available memory. Bottom line (usually): More frequencies=more money.
How far should the range be?
Most (if not all) railroad communications are FM and are limited by "line of sight", meaning that transmissions will only reach about 50 miles at best
depending on the terrain you're located in. Hills, heavily urbanized areas (large buildings) and even trees can limit the range of transmission. Additionally the output power of the transmission will limit the range of reception.
I'd suggest you read the threads I've mentioned above-all of your questions have already been answered along with some general guidelines on purchasing a scanner.
BTW-A couple of other things to consider-if you plan on carrying your scanner trackside on railfanning forays in addition to memory, you'll want to think about battery life, portability and durability.
Batteries do run down, usually at the most inopportune time. Additionally when carrying a scanner trackside they tend to be dropped with an alarming frequency. If you're considering purchasing a portable (hand held) scanner find one that can attach to a belt or fit in a protective carrying case.