For moisture or sampling?
We use a moisture tester from New Holland, and a core sampler for feed tests that we picked up from ENasco. It goes on a cordless drill and will pull samples right through and into the core of a 6' bale.
for moisture testing i use a probe from john deere. I would suggest getting the one with a cord from the probe to the tester. They make some with the probe and tester all in one but if you break the probe you got to buy a whole new tester not just a probe. If it is for sampling, i got about 2.5 ft metal probe with teeth on one end and then you take it off and the hay falls out. If your bales are tight a cordless drill wont last long. I use a portable air compressor and put it on an airdrill.
Moisture probes are a must for baling....knowing hay is being put up right is a must for quality.
The next step is forage testing...whether for feeding or selling it is one of the best investments you can make. We've used a neat little sampler for years now. It's just a simple push in & pull out but you can random probe an entire stack in just minutes and it'll hold the core sample of about 20 bales. I prefer it over the screw in type (either brace & bit or drill powered. )
I have not found a moisture probe that I like or trust for that matter. I use onefrom john deers now but I trust my hands more that it. Even bought a really expensive demherst which is supposed to be top of the line and it was always screaming 25 moisture when it was bone dry. As for a core sample I like the colorado hay probe. It is a smaller push in type probe and gets more leaves than the screw in type probes. It also has a container on the back so you can probe an entire stack before pouring it in your sample bag. Its much easier to use than taking off the probe every stab to empty it.
The probes that you drill into the bale are the best. You get a more accurate test. We have both, the Colorado probe and one that you put on a cordless drill. You get more leaves with the drill probe than you do a push in probe. The only down fall is they don't work to good when your battery doesn't work on the cordless.
We do some custom haying so we've gone through a couple moisture testers, lol. Theone piece we had from New Holland worked good, but it was big, bulky, and one piece. It got lost at the eld of last years season. The one we use now is a two piece Agco one. Works awesome. It seems to be a little more accurate and consistent in the readings then the New Holland one was.