Which altcoins are best for small payments in terms of transaction costs and speed?
I think right now raiblocks is the best in term of cost and speed, only a matter of time before people start using this more. Litecoin is also very good for sending small payments and there's quite a lot of places that accept litecoin alongside with bitcoin. I only use that two if i can because it's always cheaper and faster rather than using bitcoin or ethereum (especially when the network is clogged).
Yes, I agree with you, raiblocks is the most ideal option, but not yet at all stock exchanges it is. Over time, I think it will be fixed.