Since BA no longer fly to anywhere in Germany from LGW, I use Easyjet a lot (mostly to CGN). We used online check-in for the first time in May (late May Bank Hol), as my other half was in a meeting that afternoon and she may have been cutting it fine. As it turned out we were in plenty of time - short queue and changed to boarding group A at the desk. If the queues at check in had been horrendous (and at 4pm on a Friday afternoon, they often are), we'd just have slummed it in D. By the sounds of it, that's quite a common strategy.

And as alluded to above, if they use gates 3 or 11 (where there is no holding lounge), it really is first come (to the boarding gate), first served.

So, use online check-in - you really can't lose!