Pellets are like 30 bucks or so and last 4-6 months. I forget the price of GFo but they need replacing every 2-4 weeks. Also if you have a heavy bio load and/or feed heavy, pellets are better suited at nitrate removal vs GFO.
However from what I gathered if you plan on primarily softies and/or lps, pellets aren't necessary as both feed off nitrates. Sips dominated would benefit from pristine water, which would be achieved from pellets.
Or I may be totally wrong. But that's what I gathered during my research. However if you decide on pellets do it now, as others stated above me.