OT: ELF vs. A.OUT

["Josh 'Gage'" <antgage apk net>]

Pardon Me, this isn't the best place to talk about this, but here goes.

I've heard that there are binaries built in 'Elf' format as well as
'A.out'. I know if i compile using gcc 2.97 without and output name i get a
file named a.out... 

whats the pros and cons of these formats? if elf is better, how can I
activate that or recompile with it into gcc?