If you can wait and donate when there's a particularly good matching opportunity (for example the Facebook match on Giving Tuesday), you'll end up giving a slightly higher total that way. The big downside to this is that it's much easier to set up a standing order and not cancel it than it is to make a large annual donation on a particular day while focusing on where to get the best match for it.

The other advantage of a standing order is that it keeps you connected to the community. I set up a trivially small standing order in 2012 while I was still a student, and I think it played a part in keeping me aware of the community, with me ending up getting increasingly involved over the last few years (and now donating more than 100x more).