Rookie questions - toneam and cartridge

Hi all! I'm fairly new to the analog scene and I'm hoping I can get some good advice. I recently aquired an older JVC turntable. I know that's not a name that inspires any awe in the turntable world, but this model (QL-Y66F) seems very well built and in excellent shape. At any rate, it's just an experiment for me...

My first question regards the tonearm. The unit came with two tonearms - one S-shaped and the other straight. The manual mentions them both but says nothing about why one would choose one over the other. Can anyone give me some insight here?

My second question is about the choice of cartridge. Currently the unit has a Shure M91ED. I have no idea what the condition is, but I have found several place which stock replacement stylii for this cartridge, so it would be easy and cheap enough to freshen it up. The question is whether or not to bother. Is this a decent and appropriate cartridge for the turntable or should I look into another cartridge altogether? And if so (new cartridge), what would be a good suggestion in an inexpensive cartridge? I don't want to over-equip the turntable in terms of a high-end cartridge. If I decide I like analog enough, I'll likely dump this turntable in time and pick up something better.

Thanks for your suggestions,
RLW