They are both pretty stable.
I've built 2 PCs for other people with the MSI Neo4 Platinum (Ultra) and not had any issues. One asked for DFI, and that went great as well.
Although, I never owned an Ultra myself - I have had bad experiences with the MSI SLI version though.
I started with an MSI K8N Neo4 Platinum SLI, it was stable while it lasted, but it did eventually die after a BIOS update. I should have RMA when I first installed it, as I noticed SLI was very problematic on it - possibly due to the PCB card it uses. (Never had an issue with the DFI Lanparty SLI-DR yet).
As for stability - they are both pretty solid IMO. I'd go with DFI honestly, seems like you get more bang for your buck.