Package just means the "shape" of the component, e.g. whether it's designed to be mounted through-hole (as you would on a breadboard for example) or surface-mounted.
Speed is exactly that - how fast the clock oscillator can run (which affects how quickly the '85 can execute instructions and perform other tasks).
For example, I have the ATtiny85-20PU. They are 8-pin DIP and will run up to 20MHz, although in my setup I usually have them running at 8Mhz as it's more than enough for my applications. If in doubt, those are probably the ones you want for prototyping with!