Bit of an opinionated question, but ild go Slingshot over my republic without a doubt. If iver of them would be my first pick is a totally different question all-together though.

What are your requirements?

Maximum speed, I live in Auckland. One thing is this guys. My head is hurting who do I go with...

Are you getting voice service?  Would you use the router they gave you, or do you have a nice router you want to keep using?

Unfortunately it looks like TrueNet don't have enough probes on Slingshot fibre to show how good the performance is, but the last report makes MyRepublic look pretty dire: https://truenet.nz/story/2016/03/february-2016-urban-broadand-report

I've personally have had no problems with Slingshot. Haven't really tried MyRepublic though, so I can't give any feedback on them.

Was with Slingshot for years before UFB arrived in Hamilton. I would rate MyR no worse than Slingshot, perhaps I would rate them better as the online chat support is helpful and fast to deal with. Most of my dealings with Slingshot on the phone have been rubbish.

Performance wise I have no issues on 100/50 and 200/200 having moved from Orcon UFB a couple of years ago it is the same.

I'm happy with MR.  Only time I tried slingshot was 5 years ago on ASDL and it dropped out a lot at peak times.