Audio quality wise they should be precisely the same. All lossless digital. Latency... man I have looked and looked to try and get a technical answer but I can't. The lack of proper engineering data on audio stuff drives me up the wall some times.
So all I can tell you is from what I know about the underlying technologies:
MADI is based on FDDI and CDDI. These were 100mbps synchronous ring networks used a decade or more ago in computer networks. Because of the synchronous nature of operation, it makes some logical sense for audio data. It doesn't look like there is much overhead on the signal, so there shouldn't be a lot of latency. While FDDI itself was fairly high latency, that was because of the ring nature, data passed through all connected hosts. MADI is point-to-point which will keep latency down.
Dante is gigabit Ethernet. That is a very low latency interconnect. With a good adapter you can see times of 100 microseconds, and that is with the overhead of the TCP/IP stack. For pure Ethernet frames, as one would assume Dante is using, it is lower. However this depends on packet size, this is for small packets, and also assume no retransmissions. Plus Dante is switched, just like regular Ethernet, and switching fabrics add latency. That said, it should still be very low. As an example if I ping the webserver here at work with a 1500 byte packet I have a latency of about 1.4ms. That is the time it takes for the data to get through my TCP stack, to my NIC, out through 3 copper gig switches, over 10gig fibre to the layer 3 access switches, to the core switches, to a different access switch, back to copper, in to the web server, up its stack, and then all that back around again. Moving to something close on the network and in this building, the time drops down to below 1ms. This is on a standard, public, shared, network.
So, it would mostly come down to implementation on the soundcard. The interconnect technology itself shouldn't have a substantial impact.
How are they in practice? Wish I could tell you. I haven't been able to find anything on that.