From an outsider's perspective, SFR based designs look like hellish machines which are begging to burst up in flames. In contrast, I love the design of the properties LFR, except the material problems of high temperature lead. And in German circles the Dual Fluid reactor gets a lot of buzz as well.
I have a tremendous love for the fast breeder reactors (particularly Superphénix); that we had that technology so long ago astounds me. However, I recognise that they are technically challenging.
From a modern, pragmatic point of view, I'm very partial to SMRs and AMRs (advanced modular reactors). They are also easier to implement on non-technical grounds (e.g. site permissions).
Lead-fueled reactors are definitely an interesting area, and Russia is in the process of building a 300MWe demonstrator (BREST-300-OD). That being said, they have their own share of problems.
Startup and maintenance is going to be a beast, slowly heating up the reactor to working temperatures is going to take almost a year. The other problem is that it's still not clear if corrosion problems can be solved satisfactorily.
Reactor construction steel is stainless because it has a protective film of oxides on its surface, and lead gradually rubs it away (and then rubs away the construction steel, at a much faster pace). BREST-OD reactor designers spent a decade perfecting a system that is supposed to manage the amount of dissolved oxygen in lead, but it needs to be tested in the actual reactor conditions. With all its crazy temperature gradients and flows.
Another interesting area is light-water cooled breeders. Such reactors _are_ possible, but just marginally. And they have the nasty positive void coefficient, but it looks like it should be possible to compensate for it.
From an outsider's perspective, SFR based designs look like hellish machines which are begging to burst up in flames. In contrast, I love the design of the properties LFR, except the material problems of high temperature lead. And in German circles the Dual Fluid reactor gets a lot of buzz as well.