Keyboards with excellent sounds are often expensive. Midi Controllers are relatively cheap and there's many excellent sounds via software such as FL Studio. I've tried using FL Studio live before, but I think due to it being such a large and finicky program, it's had errors, and you can't exactly debug your keyboard during a live show. Does anybody have any suggestions for using a Midi Controller live, or advice on what software they use?
I personally prefer to use hardware synths. The software synths require a high end computer in order to not choke on the sheer amount of data. Even using the most powerful laptops available (within reason), I've still run into issues in the middle of shows. The dedicated hardware of a hardware synth completely avoids this issue. For programming, I use my own software, Cadenza, though I wouldn't be surprised if other programs have the ability to communicate with hardware synths as well.
The core of a successful live show, in my experience, is the same regardless of what equipment is used or what type of show it is: preparation. Whatever controller(s) you have you want to learn like the back of your hand and practice with them daily. Setting up mappings, presets, defaults, and saved sessions that are ready to go as quickly as possible is an important part of preparation with a controller.
Ideally you want to plan and determine what you want to be able to do, then put in the hours configuring and tweaking the settings on the controller and software until you can do those things, and finally practice, practice, practice until you can run through a mock show knowing exactly what your next move is.
Having a backup plan is also good. If you have a basic synth keyboard that has some sounds in it that you also use as a controller, then you can use the built in sounds if the computer goes down. Or you could look for an affordable hardware synth module. Likewise, an inexpensive controller with a limited range of keys and fewer controls could help you finish the set if your excellent full featured controller stops working during a show.
Matt has covered the software options I was going to cover. I will say that Live might have a bit of learning curve but it is very powerful for doing things that can't be done in Mainstage. Mainstage has better overall sound quality IMHO. You should be able to use FL Studio effectively in a live situation also, just expect it to be like learning a musical instrument (because that's basically what it is) in terms of practice time.
I've been a bit around the block and here is my story.
I used to produce a lot of music in my home studio, so I wanted to bring those exact sounds with me live. For quite a long time my setup consisted of either Logic Pro, some softsynths and a midicontroller. Later Logic Pro was replaced with Mainstage. The possibilities where endless. So was the risk of errors.
I found myself spending more time tracking midi cables and setting up controllers that had somehow been mapped wrong than actually playing music. My band was always making fun of me because I could never get the right sounds on time and generally while the setup sounded better than most digital hardware synths of the time, it was too much of a pain to maintain and prepare.
I felt like I used huge amounts of time on this, but being honest with myself I've never been the kind of person who prepares a lot in advance and most of the time was probably spent very inefficiently. I was often trying to set up stuff while the rest of the band was waiting and often making poor decisions due to the stressful nature of the situation. If I had spent some of that time setting things up in advance instead, I would probably have had better results.
Then at one point I bought a Nord Electro 2 and quickly fell in love with how easy it is to program on the fly. I hooked it up with an extra keyboard to be able to play with two manuals and relied fully on it for my base sounds ...well, until I needed a synth patch. Suddenly I had to wire Mainstage back into the mix and issues immediately started cropping up again.
So I sold my Nord Electro and went out and got a Nord Stage instead. That was the best purchase I have ever made! It is a 1st gen so it is getting pretty old, but the fact that a new Stage costs so much and this one sounds so good still means that I cannot justify buying a new one yet. I still play the majority of gigs exclusively on this board. The philosophy is the same as the Electro. It is quick and easy to program on the fly. Obviously I have presets for most songs, but if we are rehearsing a new song and I realise that it would be nice with some organ over the chorus, it's just a matter of pressing two buttons. Something I never was able to achieve with a computer based setup.
Another thing is the ability of a sound to cut through a mix. In a live situation there is usually not a lot of time to do anything else than levels mix-wise. Whenever I try software piano libraries, they sound great on studio monitors and headphones, but once they are playing through a PA they sound like shit and really can't cut through the mix. The sounds on my Nord was designed for this and they almost always work on any PA without much EQ'ing.
If you prepare really well, I'm sure you could run everything off a laptop with good results. But there is a lot you need to think about. First, you need a good audio interface. Running a 10-15m minijack out of your computer wont cut it. Then you really need to work with setting up a good midicontroller to your preferences. You probably want to map the controls so you always have fx. filter cutoff on the same place. Besides having "full patches" with all the sounds you want for a certain track, you probably want to do some template patches with some of the things you commonly use (i.e. a piano/synth split, maybe piano and strings layered, maybe a bass synth and an arpeggiated synth) so you can have some degree of instant gratification when playing rehearsing. You have to think about "mixing" your live mix on a PA, figuring out where the problematic frequencies might be and EQ them out and you probably have to apply some compression as well to make everything sound even. Also, it is extremely tempting to keep adding extra layers and synths "because you can", when you have a setup like that. Don't do that. Everything you add to the setup is a potential source of errors and as you mentioned yourself - it's not much fun debugging a computer on stage.
In terms of having a powerful computer, that certainly helps, but I started doing this 10 years ago and I was ok. Computers have obviously evolved a lot since. Avoid the crazy fancy new top-of-the-line softsynths that are usually CPU hogs - and go with something leaner. I used to mostly use the built-in plugins in Mainstage and maybe a few specialised plugins.