I would vote the E1 M4...
mainly because its different, manuverable, and an M4 that has a large battery type. M4 all the way E1's are extremely upgradable and more reliable than CYMA I believe. Even though CYMA has steped up there game I still trust E1 more.
The CYMA SOC 16.... I know what your think its a shorter M14 meaning its got to be more compact..... WRONG my buddy has a TM SOC 16 its longer than an M4 with the stock half way out. Also im not sure how upgradable the CYMA SOC 16 is.
Go with the E1 M4 in my opinion