Using gigabit here to as many devices as possible.
In my opinion use at least gigabit to your core/hybrid.
MDs will work on a 100Mbps connection (just little slower boot time).
If you really must use 100Mbps, make sure you get duplex settings correct since it tend to work pretty well but not 100% correct all the time.
With gigabit, duplex settings is part of the standard. It should work and so far I haven´t seen any gigabit connection that have gotten wrong settings when negotiating with a gigabit switch.