We ring some and not others. The wethers are more likely to put on a layer of fat than the entires, so on the whole we think we do better with entires that will finish before about mid-August. However, once there are hormones in the air, the entires do tend to stop, and depending on breeding you can't always just keep them through to the New Year as they may be overbig (the frame keeps growing, it's the flesh that seems to stop) by then.
So we basically tend to not ring single males until those born in the last few weeks, and to ring males who are twins unless they are born very early and/or are stonkers. Broadly.
I prefer all the pet lambs to be castrated and usually don't achieve it, as there are always one or two that become pets at more than a week or two old.
The other thing to consider is can you manage entires if there is some disease or other problem (abattoirs close, meat companies go bust, labs let viruses out in the drains, etc etc.) that stops you sending them away, or a local problem that stops one or two being fit enough to go (illness, strucken, lame, etc.)