I have bundles ultisnips and youcompleteme installed on my macvim.
The problem is that ultisnips doesn\'t work because tab is bound by ycm.
I tried putting let g:UltiS
I personally chose to not use with YouCompleteMe but navigate it manually.
So I added this to my .vimrc:
let g:ycm_key_list_select_completion=[]
let g:ycm_key_list_previous_completion=[]
which simply disables the tab key for YCM. Instead you use the movement keys (arrows or CTRL-N/CTRL-P) and select the entry with CR. UltiSnips works default with tab.