Any difference between 早安 and 早上好?
From the accepted answer at Baidu:


  Both are words of greeting. Nowadays people generally use “早上好”. “早安”
  will give a feeling of before 民国 (the Republic of China (1912-1949)), 
  or a literary feeling (it's common in literature).


Other people think 早安 has a warmer feeling.

Of course this is the perspective of mainland people.

In Taiwan 早安 is used much more than 早上好. （Ratio: 28, Google advanced search: exact phrase, country TW, language zh-TW)


"早安" 5,340,000
"早上好" 192,000


In the mainland, incidentally, 早安 is also used much more than 早上好, although the degree of usage seems much closer. （Ratio: 2.3, Google advanced search: exact phrase, country CN, language zh-CN)


"早安" 24,500,000
"早上好" 10,400,000