A direct-to-PA rig has a lot to recommend it. Put together a floorboard processor and some in-ear-monitors (IEMs) and you can play any venue that has a decent house PA. Let's not forget the cost and weight savings: that's good for the wallet and the back. It's all very tempting... But there's a lot more to consider than just cost or flexibility or "cool factor"...
- How many different sounds do you have to cover?
- Are you in control of your choice of sounds, or is someone else (e.g. a musical director) dictating that?
- How much time do you have for setup/teardown?
- What kind of venues will you be playing?
- How much space do you have on stage (or in the pit)?
- Will you be traveling with this rig? Domestically or internationally?
- Can you run a stereo feed to the PA?
- Are your IEMs mono or stereo?
- Will you have control over your IEM mix?
- Can you get a decent monitor mix?
There are probably other considerations, but that's a start...
Here's why I asked these questions:
How many different sounds do you have to cover?
Are you in control of your choice of sounds, or is someone else (e.g. a musical director) dictating that?
These have to do with matters of sonic flexibility. If you get to call the shots and pick your own sounds, and you can live with the sounds you'd get from some kind of amp sim plus traditional pedals, then a custom board might be the right route. You'd get to pick exactly the pedals you want for your effects rather than having to "make do" with a collection of modeled effects.
OTOH, if the sonic requirements are imposed by someone else and are likely to change from gig to gig then a modeler (and a set of good programming skills for your modeler of choice) would be the way to go.
How much time do you have for setup/teardown?
What kind of venues will you be playing?
How much space do you have on stage (or in the pit)?
Will you be traveling with this rig? Domestically or internationally?
These considerations go to the physical attributes of the gear. Complexity works against you if you have to load in and play on short notice. Likewise, a larger rig is more of a liability when travelling, especially given the current state of air travel. A computer-based rig might be a great solution for flexibility and compactness, but would be at risk in a rough environment.
If you're going to be travelling internationally, it would be best to select gear having a universal power supply (or at least be able to carry enough country-specific separate power supplies to cover your needs).
If you're going to be travelling at all, you should think about your contingency plan. What happens when some component of your rig fails? Will you be able to buy a replacement no matter where you happen to be?
Can you run a stereo feed to the PA?
Are your IEMs mono or stereo?
Will you have control over your IEM mix?
Think about how you're going to interface to the house systems, both for FOH and monitoring. Stereo is nice, but not that important if the house expects a mono feed from your rig. OTOH, stereo could be useful even if the house takes a mono signal from you. If you have control over your own IEMs (i.e. using a local mixer) and your IEMs run in stereo, then it might be nice to monitor in stereo for a better sense of ambience. (Personally, I hate IEMs. When I turn my head or move to a different spot on stage I want to hear the sound change...)
Can you get a decent monitor mix?
A venue that deals regularly with touring bands should have multiple monitor mixes. A really good venue will even have a dedicated monitor engineer. In this case you shouldn't have any problem getting a good feed to run to your IEMs. (Or if you share my distaste for IEMs, just get a good mix to your monitor wedge and be done with it.)
A smaller venue may only have two monitor mixes: one for the drum position and another shared by the rest of monitors, usually lined up along the front of the stage. In this case you're going to have to improvise whether or not you use IEMs. The drummer's monitor will carry whatever the drummer needs to hear, while the singer usually gets priority for the rest of the monitors. Neither of those feeds is likely to do you much good. You may have to use just one earbud, or mix a stage mic into your IEM mixer. You could even rent (or bring) a powered monitor for yourself - it's not quite as convenient as relying on the house for monitoring, but it's no worse than carrying a guitar amp.