Russ, this is a tricky topic to discuss, and like most things in music, mostly subjective. So many things can influence your approach to performing. A few, off the top of my head, are:
1. how strong is the economic motivation? how much do I need to maximize the income opportunity?

2. How important (to you) is the pleasure derived from musical collaboration? Obviously, some here prefer the total control of performing solo. Control of material, control of arrangement, control of tempo, etc.

3. Ego. Some people actually prefer to be the center of attention, and not share the spotlight. This is NOT necessarily a BAD thing for those in the entertainment field. I've found that these types lean more to the 'entertainer' side than the 'musician' side.

4. The availability of good local musicians. Some, simply don't live in areas where good, compatible, musicians are in abundant supply.

5. This is subjective, of course, but I don't agree with Gary's view that using an arranger is more 'versatile'. In fact, that is the precise reason that I don't use one. I love the freedom that non-programmed anything, gives you while performing. Although it's more demanding, I love being able to just launch into a tune and, if everything feels right, just 'going for it' and taking the tune to new places each time you perform it. I admit that this is probably more of a jazz thing, but not altogether.

There are, of course, many other considerations, and as usual, you should pick the one that works best for your circumstance. I don't play as often as most of the others here (usually once a week and only in jazz clubs) and at this stage of my life, lucky enough to be able to pick and choose both the gigs and the people I work with. Luckily, I also live in an area rich with quality musicians. I've never tested it, but I doubt if any of them would be willing to work in an arranger setting (using styles, mp3's or midi files). What I can say is, I haven't had as much fun in years as since I got my Nord C1 and going back to gigging as a jazz organ trio w/vocalist. I've toyed with adding some other 'voices' but in the end, decided to stay true to the format and being satisfied with the occasional 'guest' horn player. YMMV.

chas