Smoking, nothing in this word is guarantteed. Problem is, to be totally effective, encription needs to be 128, (in theory, it can not be cracked), I doubt that one, but that is what programmers tell me.
However, it is against US law to send encripted mail over international waters @ 128 bit encription, now who regulates that, it is anyone's guess. In fact, a good reliable programmer whom I know works for the government, and he states that USG has to the right to read ANY email crossing over international servers.
So to answer your question; encripted emails are more secure, but if a hacker, g man, or someone else, who is inexperineced in cracking encripted email grabs your message, then chances are they will not be able to read it with out proper encription keys. Even though people say, "It can't be cracked", remember there are guys out there that write this stuf, and chances are they can crack it because they know the code.
That is why Mr. Gates with MS, does not allow any of his programmers to know the ENTIRE code to C 2 OS's like NT, 2000, XP etc. He has different "teams" that work on specific parts of the OS's codes but no one but himself, knows the entire programming code for his C 2 O's.
This is to lessen the chance a hacker or a programmer can look at flaws and vulnerbilities in the actual hardcore code itself.
Take a look at the hard drive and computer they found over in Alfganistan, when this war started. How do you think they were able to obtain all that info. Deleted and encripted documents were found and decoded to read and gather intel.