Best investment; cartridge or line stage?

Phono stage  just go with a Denon DH-103 cartridge and get the wood body for it and you are all set.

knock1

I am supposing OP has Rega Ania which has an Elliptical Stylus on aluminum

The reason is simple: the tonearm's ability to properly track the cartridge far outweighs what cartridge you have. The better the arm is at this, the less differences you'll hear between cartridges assuming they are set up properly.

So absolutely true! Not only does a great tonearm allow for proper tracking, but a great tonearm has a sound of its own due to how it handles vibrations from the cartridge. There is not a tonearm on Earth that neutralizes all stylus induced vibration. Perhaps only 5-10% of the overall sound quality comes from the material and design choices but they still count. When I switched to Reed 3P tonearms the SQ change was revelatory. 

After the choice of tonearm, invest in the phono stage before cartridge. There are so many great sounding sub-$1500 cartridges. And as noted above, cartridges are subject to wear and to accidental damage. 

@elliottbnewcombjr you are correct the cartridge is an Rega Ania.

So another really great point a couple of you brought up. Cartridges do wear out, other investments not so much. I knew I would get some great input from this crew. Thanks so much!! Time to go dive deep on tone arms.

Glad to help. Since we are agreed that only a very good tonearm can hold a cartridge at the correct angles, it is essential for that tonearm to be adjustable in order to optimize the cartridge that you have (now or in the future).

In particular: vertical tracking angle of the stylus (VTA); rotating the cartridge parallel to the tonearm (azimuth); and of course, tracking force (VTF, which most tonearms do well). Azimuth adjustment is what really separates the best from the rest, IMO. I can hear adjustments down to about 3 minutes of arc on my air bearing table and arm.

My experiments show that about as important as azimuth adjustment is resonance control, or damping, as @fsonicsmith points out. You can spend big bucks on tonearms that don’t look like they’re damped very well, so beware of that. Reed has a nice comparison of tonearm materials on their site. And I can assure you, Panzerholz sounds GREAT, no matter what some of Reed’s panelists said.

An exciting time for you. Good luck!