Analog scopes basically use CRT screens, basically a bench unit that has the settings/adjustments on the same panel as the display… Signals were modified using resistors and amplifiers then sent to a cathode ray tube for display. This was the “old” method for scopes much like an old television. Today everything has gone digital, even the new bench units. The digital scopes make snap shots of the signal very very quickly, then put all the snapshots/samples together to draw the signal on the screen.
For automotive applications, it is recommended to have at least 4 differential channels (In my opinion). Honestly, I prefer 6 but as the channel count climbs, so does cost. Differential simply means the scope measures the voltage diff between the positive and negative/ground probes for each channel. Some scopes tie all of the negative/ground leads together which can corrupt certain signals when multiple channels are used. Perfect example would be looking at analog/VRS crank position and cam positions signals at the same time. Obviously today with variable cam timing, being able to review crank and cam signals simultaneously is very important for some vehicle diagnostics.
Having fully differential channels will also help reduce channel “Cross talk” when looking at ignition or injector driver pulses. Cross talk is simply when you see the electrical signal of one channel displayed on another… There are multiple reasons this can happen but having the channels fully isolated reduces the chanced significantly. I can say the use of non isolated channel scopes on current diesel engines will not go well as the injector control use high and low side drivers. For you to see the injector pulse, the scope must measure the positive injector drivers and negative injector driver. If the scope channels share grounds, the LOW side injector drivers would be shorted together… This cause measuring issues plus have the potential to fry equipment.
Another benefit to Digital scopes is that the user can make recordings/snapshots of signals on most modern units… This is very nice when trying to capture glitches or build yourself know good/bad signal library. Digital is the way you likely will be find yourself going. You will want to also pay attention to scope sample rate, voltage range and the number of bits per channel. Sample rate is how fast the scope is collecting data. A scope too slow will be unable to see some signal glitches or may cause some actual good signals to look glitchy. For example, when looking at a modern day digital/Hall type crank sensor on a high resolution trigger wheel (60 tooth) the signals will look pitiful even at idle on a scope that does not sample fast enough.
The voltage range is important because you don’t want to fry your hardware by over voltaging. Keep in mind, when looking at an ignition coil primary signal. Voltages may exceed 200 volts, Fuel injectors as well will have high fly-back voltages. Modern diesel do exceed 200V. From experience 200V should be the MINIMUM voltage range you should consider for an automotive scope.
I am rambling, so time for me to shut up. Back to your question, make the investment in a good digital scope.