Lendl is definitely ahead of McEnroe and Connors, however I think the latter two are close - have a look at Open era rankings that I link to in the first posting in this thread.
http://tt.tennis-warehouse.com/showthread.php?t=463381
I didn't put any of these in tier 1. Borg is confusing because of his truncated career. If you look at my rankings he is about the same as McEnroe - but he is regarded as superior due to the number of majors he won. Regarding McEnroe and Connors - McEnroe's WCT finals wins often get swept under the carpet - they were a very big title back in the day - and are now largely forgotten. I am a big advocate to giving players credit for winning events that were big AT THE TIME THEY PLAYED THEM regardless of how they are regarded now. People have short memories. I am sure that at the time McEnroe was much more focused on winning WCT finals than he was Australian Opens. His 5 wins there propel him ahead of Connors slightly.
On balance though open era tier 2 is probably in order like this : Lendl, McEnroe, Connors, Agassi
Djokovic I believe will join them by the end of 2014