Wormholes

If you close all open holes, as you should, then a big system is better. Without a new sig, nobody can come in unseen, so you are safe. If there is a new sig, they may be out of range, so have no way to know you are there, but you do know that there may be danger because you see the new sig.

In a C4 or C5 where you farm with a Marauder and/or are scrammed by sleepers, this is most important. If the incoming hunter does not see you when entering system, he'll go through the usual routine first and you'll have enough time to exit bastion mode or kill scrammers after you see the new signature. If he sees you immediately, you'll probably have no chance.

C3s shouldn't have so many holes open all the time, having just the one static. Sure, it happens, but not like every day. Some holes are also easy to close, like the X702 from Hisec with only 1b mass.

It helps to keep the system bare of content, so farm regularly. If there are no sites, or just one or two, people connecting to your system may even close the hole for you because your system is useless to them.