Even ack is fast, it still takes a few seconds when I search something inside my rails project. I hate waiting. If Ag can work with same options as ack, and with ack.vim by simply creating symbol link, it'll be great.
Btw, I noticed the output of ag does not highlight matches and include line numbers. Maybe those are what make it a lot faster?
I don't know how you're running Ag, but it should highlight and print line numbers like Ack.
If you had read the README, you'd know that Ag is faster than Ack because it uses tricks like mmap()ing files, pthreads to take advantage of multiple CPU cores, boyer-moore-horspool strstr(), and PCRE's JITed regex engine.
I don't use vim, but some Ag users do. There's an ag.vim: https://github.com/epmatsw/ag.vim