Indeed DIL is DIP and the 168V is the lower voltage version, requiring a minimum of 1.8V instead of 2.7V.
Furthermore, the first (20PU) runs at a maximum of 20 MHz, the second (10PU) will run at a maximum of 10 MHz.
At this moment the difference does not matter for you, for the internal oscillators are the same, but I'd take the 20PU version because of the possibility to run it at higher speeds with an external crystal. You never know when it might come in handy.