NI myDAQ has an input sample rate of 200 kSPS and bandwidth of 400kHz, where AD2 has 100MSPS and 30MHz+ (with adapter) => point for AD2
NI myDAQ has maximum input voltage +-10V, where AD2 has +-25V => point for AD2
NI myDAQ has an output sample rate of 200 kSPS, where AD2 has 100MSPS => point for AD2
NI myDAQ has maximum output voltage of +-10V, where AD2 has +-5V => point for NI myDAQ
NI myDAQ has a built-in multimeter (so it is able to measure in addition to voltage, also resistance, current, diode voltage without any additional adapters) AD2 requires separate adapters for such measurements => point for NI myDAQ
NI myDAQ has fixed +-15V supplies (32 mA) and +5V (100mA), where AD2 has 0...5V and 0...-5V voltage outputs (700mA max with external power supply) => point for ???
Ni myDAQ has 8 digital IO, where AD2 has 16 of them. Also AD2 IOs can be controlled much faster than ones in myDAQ => point for AD2
This is a fast comparison of a key features. Full documentation of each device are available here:
Summing up all above (in my opinion):
AD2 is a better choice for debugging fast analog and analog/digital circuits. A software adds a great value by allowing various measurements and tools without any need of programming. Also an interface for python scripting allows designing own applications. There is also LabVIEW interface provided. You can always see all these functions in interactive demo - just download recent Waveforms software.
NI myDAQ offers much slower I/O and less digital channels. At the other hand it can be used as off-the-shelf multimeter`. It also includes basic software and interface for LabVIEW, but lacks for example interface control (I2C, SPI, ...).
Also AD2 can be purchased in reduced price for academic use.
This is of course my private opinion on these devices - you have to decide which one to buy by analyzing use cases.