I'm a hypocrite in the matter here. I like redstone flux as a system, and I cannot say that I do not use it because that is a flat out lie. However, I personally want to see it more complex. Or at least, a little bit more? I mean, hell, they gave the machines tiers in TE4, why not use that as an example of energy tiering, same goes with the various conduits/energy ducts(?) out there. Like, there could be Low RedstoneFlux (LRF), Intermediate RF (IRF), High RF (HRF) and Resonant RF (RRF). That's four tiers to go with the four machine tiers.
Of course, that would mean that resonant energy ducts would have to be a thing, but I remember reading once that somebody would rather want that late game anyway. And with this, there'd have to be converters, and dynamo changes. Steam dynamos/survivalist engines/stirling generator/other early energy producers would supply you with LRF, and the same pattern going with what you'd see fit, probably the RRF power producing tier would include things like the reactant dynamos and big reactors and all that fun stuff. Cells would probably need upgrades for like, how much energy they can store at the price of the speed of filling up, because, well, the tiers should probably effect them too. The only thing that'd probably accept all types of RF would probably be the capacitor banks from Ender IO, and the same for MFR machines, but you'd need converters if you want to take the energy out or put them into machines (see below). Also energy loss should be a thing with ducts, with the lower tiers being the most notable. The highest tier would still have a energy loss in distance, but not something to worry about like you should and would with the previous teirs
With the tiers, you can't say, use HRF on a basic machine, otherwise that would overload said machine and possibly fry it. No explosions, just the inner workings of the machine just, stop working and the machine could very well turn back into a machine frame, losing whatever you have in there, upgrades, whatever you're doing, etc. Using LRF on, say a resonant machine is inefficient and with that example, it'd probably be a fourth of the energy going in, or it may drain the LRF without even accepting it.
To solve the problem of "hey! everything got fried! how can I use RRF in my basic machines u ruined my system everything got destroyed I hate u!!!11!11!", there'd be converters for every tier to every tier. LRF to IRF would be a 4:1 change, LRF to HRF would be 16:1 and so ons, the amount of energy required to convert going up by x4 per tier. IRF to higher iterations would be by x3 the amount per tier, and finally, HRF to RRF would be 2:1. And this would all go in reverse for whatever other reason you'd want to do that. For inter mod compatibility, there'd be converters between all the different types of RF to finally, pure RF, if there's a mod that would still require the old, easy system for it to run, like MineFactoryReloaded, unless they'd change it, and EnderIO and any other mod that adds a general energy storage battery. Pure RF would be about around IRF levels in both amounts and converting.
Of course, for the people who'd want a simpler sort of RF system
Unrelated to all of that, I'd personally like to see the energy go to mundane uses, like powering lights and fans of all kinds, for those times you have too much energy that you don't know what to do with. Also it gives you a reason to manage things better.
Sorry for the huge wall of text, even if it is spaced out. If anybody wants me to put it in a spoiler, I can do that.
But yeah, no single energy system when they're so easily compatible nowadays.