Definitely get one with a higher BW. Always go 5-10x higher BW than the frequency you expect to use it at.
The sample rate is the number of samples per second. Consider a 2GS/s rate looking at a 200MHz signal. 1/2,000,000,000= a sample every 500ps. At 200MHz, a cycle is 5000ps, so you will get 10 samples (dots) per RF cycle. Interpolation turns the dots into a smooth line that hopefully represents the true signal. The more dots per cycle, the more you can see the actual sine wave and not some mathematical guess as to its shape.
The bit depth is the vertical resolution. So if you get a 12-bit scope, your vertical resolution is divided up into 2^12=4096 discrete steps. Thats the number of steps the ADC has.
Also consider that the amplitude displayed is only 71% of actual at the scope's stated bandwidth, so the closer you are to that limit, the less accurate the amplitude.
You might want to see a harmonic, or might have a problem caused by such a fast rising signal that a lower BW scope might not see. The most common way to measure scope bandwidth is to inject a square wave with an edge faster than your scope can draw and see what it does draw. The rise time and bandwidth are related by the formula rise time s=0.35/BW.
Your choice in BW should not be based on the most common signals you will look at, but rather on the fastest signals you might encounter (and how much of the actual waveform is meaured rather than interpolated).
