Look at the thread, as well as the manuals (can get them on Hakko's site in .pdf), and see which you'd prefer. Iron wise, they're the same. So it will just come down to which control method is more comfortable/useful to you.
FWIW, If you're truly interested in a digital model rather than a knob, you might want to take a look at the FX-951. It offers better heating technology (heater + sensor are built in the tip) as well as missing features in the FX-888D (sleep mode for example). Just a suggestion to consider if you'll be doing a lot of soldering. If not, skip this, as the price is $250USD (MSRP, and I can't ever recall seeing it at a discount/sale).