Honestly if you can afford it get both... or one at a time. Because there will be times when all you wanna do is top off, and the pump is perfect for that. Also like you mentioned it is very portable, but a 80 cu tank is portable too.
If you have a 3000psi. fill pressure gun, then you will probably opt for a tank sooner or later. however there WILL be times when your tank gets to 2500-2800psi. and you can not fill your gun all the way.
pump to the rescue...;)
I have a 3500psi. 80cu. steel tank that I got off craigslist for like $120 still in hydro till 2013, plus an $60 airforce din adapter completed my setup. plus $15 visual inspection, $6 fills. Tanks are nice, and soooo easy.
I guess tanks have like a 10% overfill, so my scuba shop fills my tank to 3800psi.