Wich is better for muni a disc brake or hydro brake tell me the differences. and pictures.
Both are good, and I have both.
The Hydraulic rim brake is totally independent of the hub, and cranks, so all you need are the brake bosses. Disc brakes are nice because you don’t lose stopping power if the rim gets wet, and you won’t get rim-rubbing is the wheel is a bit out of true.
But disc brakes also require a specific hub and the outboard type require bike-like cranks with a spyder attached. For those you can’t change cranks easily, but you can with the inboard type system, but if you’re retro-fitting your current wheel to accommodate a disc brake, you’ll have to tear down your existing wheel and lace up a new hub with the disc option.
just wondering i have a nimbus frame… is it possible to put brake bosses on my frame considering i dont have them already installed. if so how do you do it?
You could get this. You have to weld them on, find a welder to do it. I’m not sure which nimbus you have but nimbus MUnis already has the bosses welded on. You may have an older model that doesn’t have them?
http://www.unicycle.com/magura-braze-on-brake-kit.html/
i dont know if i have an older model frame but it is a nimbus 2, 24" inch chrome. thank you i really appreciate your help.
Not to add to the confusion, but aren’t most disc brakes on unicycles hydraulic? 
Perhaps the question should have been between rim brakes and discs? There are significant advantages and disadvantages to both. From a riding point of view (without regard to cost or hassle), disc seems like the better choice in general for unicycling, since it’s not reliant on the trueness of your wheel.
There was a Nimbus II muni without brake bosses, before the Nimbus munis changed to 42mm machined bearing caps.
As for the original question, rim brakes work fine and are cheap (for a used Magura off ebay, or even use a v-brake). Disc brakes are the “latest thing to have” but I can’t see the point of spending loads of money to fit one - and they look a mess IMO - rim brakes are much tidier 
The main advantage I can see of using a disc brake on a unicycle is if you’re using the same frame with multiple wheels of different sizes. The rim wear you see on bikes with rim brakes doesn’t seem to be an issue on unicycles in my experience - you don’t tend to brake hard.
On the other hand, a bearing-cap mounted disc brake with external disc may be easier to retro-fit to an existing frame than rim brake bosses.
Counterpoint:
Brakes get hot under heavy use, and unless you’re riding across a lake or in a hurricane, a wet rim isn’t going to be an issue for long. If you live in a perpetually wet region, consider a different brake compound.
An un-true wheel can be fixed trailside with a tiny spoke tool. No one should be riding around with their wheel out of true.
Further counterpoint:
A disc is easier to bash than a wheel… and you can’t fix a disc trail-side.
You’re never going to need the full stopping capacity of a disc. It’s much better suited to a b*cycle. Save your money and be totally happy with a rim brake.
UK would definately be considered wet… often on rides I have not got my rim brakes to work at all - can be quite scary! it does not take much water to make them erratic. The disc is not a problem though.
Several times I have ended up removing the brakes when out riding because the wheel is beyond the tollerance where it can be pulled straight enough for magura brakes. What I will say is that a greater problem is mud. When your wheel stops rotating because of mud due to the brakes you have no choice but to remove them on the trail! Not nice really.
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I have never bent a disc on the inboard system… in 2 years of regular riding with them. External, yes you can catch them and bend them, but not common and not a great problem. It was easy to pull back to the point where it was usable.
The disc is being increased on next years Impulse and the new Orical to 180mm… this is because experience has shown that we do need better braking.
Roger
What pads are you using? Sounds like you may not have a soft enough compound.
Better braking on which setup? I agree that rim brakes on a 36er don’t do everything I’d like them to do, but I can’t imagine needing anything so heavy duty on a 24" muni (as I assume the OP is asking for). Unless you’re running 100mm cranks and riding a 20% grade…
Ironically given I live in the UK, the one place I’ve experienced this on a bike was in Utah - I think they have stickier mud there after it rains. Experienced second hand - I had discs and no problem, had to wait for my team-mates with rim brakes to declog (we ended up walking some because of their problem with this).
OR you could use a centerpull brake system:D Custom Brakes... Post What You Have! A whole lot cheaper than either of those others.