I am planning to build a rifle for varmints, and would like advice on getting an ejector or not. (I am totally new at varmint hunting, and plan for a variety of uses.)

all of my varmint rifles are single-shot without ejector. besides helping to keep brass clean it helps keep an accurate count of hits. every hit goes in the box primer up. just my $0.02.

I have both and prefer the ejector. The ones that don't have ejectors are tightnecks. This helps from damaging the case mouths.

My M700 in .223 has a tendency to dent the case mouths upon extraction unless I'm careful. I need to take a round or two out of the spring. If you go with an ejector, you may consider going with a light spring.

I'm not exactly sure what "jigger" means by keeping brass cleaner, but would be interested in more info on that.

I guess it would depend on what varmints you intend to shoot with the rifle. Prairie dogs, ground hogs and similar animals the non ejector is fine. With coyotes or other varmints that might require more than one shot, having an ejector and a magazine box can be real handy, especially when you call in a double.

with an ejector 95% of my rounds leave the table. where i shoot in texas the grass is not always "lush". consequently brass picks up a good amount of sand. unless one wipes each round clean before returning it to the box, there is a significant chance of scratching in transit.