The easiest pipe to put through that hole is going to be hard copper. If you use Lead Free solder, the joint is going to be very strong. In the old days of 50/50 you could have broken a solder joint. With Lead Free, the pipe will twist and break before the joint will.
You could also use soft copper for most of it, and use the ridgid under the rockery.
If you PEX it, remember that it's smaller then either copper or poly.
A standard copper size would be 1", even though the pigtail from the meter is 3/4"
If you only have to go a little way through, you should be able to use soft copper the entire way.
If you use poly, or PEX, you just solder on the right fitting onto the pigtail that the city has.
Some Seattle water meters have a five sided post for the shutoff key.