It's a very Rocky Long-esque move to not name the starter so that San Diego can't prepare for one quarterback when they face the Aztecs. Also add in that the previous quarterbacks under his watch were terrible such as Quinn Kaehler, Nick Bawden, Ryan Katz so one could imagine the shy trigger finger.
Of the two quarterbacks, Maxwell Smith has the upside. He was named to the Freshmen All-SEC Team in 2011, and has starting experience in the hyped-SEC. His 2013 campaign looked promising as he threw at a 57 perecent completion rate for 1276 yards, and nine touchdowns in nine games, four of those as the starter. His time at the University of Kentucky was cut short due to injury and chose to transfer to San Diego State this January.
Christian Chapman redshirted his first year of college in 2014 as he and the coaches figured that Kaehler was somewhat getting the job done. He knows the system better than Smith, but might more to put theory into practice to overtake Smith. If he continues to grow and compete, I could imagine Chapman being the solid San Diego State QB of the future.
It's still worth noting at Mountain West Media days, the roster has Maxwell Smith as QB1 and Christian Chapman QB2. And not to mention this quote from Coach Long is in the Aztec media guide--
"I think we’ll make a fairly quick decision (on a starter)," Long said.
The coaches are leaning like the rest of us towards the graduate transfer, but being tight lipped until the opener is the strategy. There is a bit of uncertainty in the air, put your money on Maxwell Smith.