Has anyone used private market investment platforms like Hiive, Republic, Angellist, Sharespost, wefunder, ForgeGlobal? Any insight as to which is better/fee comps?

Republic and AngelList generally offer early stage companies that are (in my opinion) trash. I'd say it's more like gambling than investing. I've never heard of Wefunder so can't comment there. Forge is probably the market leader but they are very old fashioned, plus they charge a lot of fees. Hiive has no fees for buyers but I think their minimum investment is higher, it's rare to see sellers with less than $50k in shares. EquityZen is another option but their fees are crazy and their share prices are always above market. The only benefit there is they have a fund that invests in multiple companies and has minimums as low as $10k. I think they're the only option for people who want to invest $10k or $20k so they are able to gouge you on fees. If you can write large enough checks, Hiive is probably your best bet. Otherwise, I'd probably do EquityZen.

I've used AL to syndicate deals that I've won but don't have personal firepower to fill my allotment. The fee is $8k which is pretty difficult to stomach unless I'm syndicating above $100k and even then it is pretty annoying. However at the same time when I talk to Cooley or WSGR or Gunderson that's about the cost at which it starts to make sense for them as well. The risk is that AL & comps blow up though and then you're stuck with your own docs so YMMV.