I'd say an intro explaining bandwidth, rise time, triggering and memory depth. For myself a person with poor vision a larger screen was a factor.
A scope is normally focused on a particular job, what are you going to do with it? is a good question to ask yourself.
...mike
That is a very valuable comment!
If you are doing a lot of work where you are really verifying results you have already simulated,you need an instrument which has accurate readouts of the parameters you need to check,plus fast setup,good facilities to export waveform displays to a PC,etc.
If you are interested in fault finding & repair of digital stuff,you need a 'scope which gives a good display of these signals,sometimes at the expense of its performance on analog signals.
A built in logic analyser would also be nice,but not at these prices.
If you are doing mainly analog repair,you need a 'scope that gives a display whether there is an input or not,so you can measure DC rails,& other DC potentials with it,but also be able to see any hum or noise on these signals.
Early DSOs were lousy at this,so many people,including myself,were "put off".
Of course,if you want to look at very fast clock signals ,& the like,that is a different animal altogether,& out of this price range.