MarkB
Legend
I wouldn't try it before the various technologies have stabilized (stopped improving). Otherwise, ship #2 passes ship #1 and arrives first.
Actually, that's also a way to send new supplies and parts, so maybe it's not a show-stopper.
Generation ships aren't a great option unless you're desperate, for a lot of the reasons mentioned in this thread. Ideally, you want to wait until you've perfected something along the lines of cryogenics/stasis/time-dilation, so that you don't need to deal with the logistics of keeping humans alive and conscious for hundreds of years in space.