There are two key differences. One is the maximum sampling rate. The DSA601 maximum sampling rate is 1GS/s. The TDS602 has a maximum sampling rate of 2GS/s.
The other key difference is the maximum record length. The DSA601 maximum record length is: 20,480 points in single sequence mode, and 32,768 in repetitive mode.
The maximum record length for the DSA602 is 32,768 points in both single sequence and repetitive modes.