Denon 103? Shure V15? AT OC9? guidance

I think the Shure is probably the most overrated of the group. The OC9 is 'arguably' the best of them, but other could have different conclusions. If you were willing to consider used cartridges which is admittedly more difficult since it requires you to find a trustworthy seller, but could yield greater rewards.
I hope this offered a little help.

My choice of the 3 would be the Denon. I'm not familiar with the phono stage in your amp. The reason I state this is that the Denon 103 is a low output MC. Can your amp handle a low output cart? If you can stretch your budget just a bit you might want to look at the Dynavector 10X4 as well.

Every phono cartridge sounds a bit different (like every microphone) and people have their own opinions. You should try to listen to several cartridges using the same LP, and form your own opinion.

For what it's worth, my experience over several decades has been that only moving coil cartridges (Ortofon and Signet) sounded better than the good old reliable Shure V15. But, it seems like every time I needed to replace the stylus of a moving coil cartridge, the particular model was no longer made, and I was offered a small discount on a new, more expensive, model. Enough of that BS. I have gone back to the Shure V15, with user replaceable stylus.

Not the DL103. The arm is not really up to it. Either of the others will work well.

I have used the older version of the AUDIO TECHNICA OC9 with great success. I talked to someone on the phone at the meddle doctor who is using the new version with the Boron cantilever. He said the new one is even better.