The ones you'll see the most are
2xERPPC and
2xLPL (I prefer one weapon on either side, but most people run asymmetrical for the shield side), followed by
3xERLL. The LPL config in particular has great sustainable DPS because it runs so cool.
You will very rarely see any short ranged builds on these, because (as you've noticed) there are other 'Mechs that do those better. Shadow Cats favor sniper configs. They have high mounts, ECM, and excellent mobility... and that's pretty much it. There aren't enough hardpoints to do anything else really well, and all that locked equipment doesn't help. Sniper configs take advantage of the areas in which the SHC has a significant advantage over other Clan mediums- namely, the ability to get into hard to reach places, avoid detection, and shoot the enemy from unexpected angles.
If you're looking for a light chaser, you're better off with a SCR or IFR. If you want a DPS machine, you want a NVA or HBK-IIC. For brawling, go SCR, NVA, or HBK-IIC. If you want a death sentence, use the VPR (I jest! It's bad, but not
that bad- there's just nothing it does particularly well compared to the other options). If you want a stealthy, highly mobile sniper, that's what the SHC does best. It's actually one of the best mediums overall in that role; there is no other medium which has all high mounts, JJ,
and ECM.
That's not to say other builds can't work... but they're not ideal for the way the chassis is implemented. You can do some fairly punchy strikers like
this one, but it will still have the Shadow Cat's huge side torso hitboxes and all that locked equipment restricting podspace and crit distribution. Compare with the same type of build on
a SCR, and you see the problem (especially since both have the same base top speed, and MASC doesn't provide enough of a boost to make a huge difference there). You don't really have the free tonnage to do large ballistics
well, nor to boat smaller ballistics. MG boating is a troll build, plain and simple, so that's out the window (though if you're feeling lulzy you
can stuff
6xMGs into your 2xLPL config and play Clan Arrow, at the expense of ECM. Not really worth the trade). You can only bring up to three missiles
or three energy, but not both at the same time because the third missile and third energy are on different RTs.
So... yeah. Energy snipers are the way to go with Shadow Cats.