All Tektronix scopes are good but they have been around for so many years that the older ones now look decidedly old fashioned.
If you can find one with a four digit 2xxx number you should be OK, even better are TDSxxxx models but these are relatively new and still fetch high prices.
Because of their age, the older ones suffer from dried up electrolytic capacitors but they are easy to repair and almost all the parts are still available. Most models have built-in diagnostics, you press a combination of buttons on the front panel and it tests itself and returns a fault code in text on the screen. My two Tek scopes are both over 20 years old and still in perfect working order, they have had thousands of hours of use and have never broken down except for ones cooling fan 'grumbling' because it's bearings were worn out.
Brian.