I fly a Saab 2000 for a living. When the pax board sometimes I stand and greet them and I am tired of the cynical comments about props and puddlejumpers and low-tech and slow and blah, blah, blah....
Most prop flights are short (very few are more than 90 minutes and most of ours are about 50-60 minutes) and frankly, a so-called "regional jet" would only be 2-3 minutes faster over those segments. I once dead-headed on an Avro in the cockpit for one of the segments we would normally fly and it was, if anything, slower than the Saab 2000. The speeds I saw indicated were not 1 knot faster than we fly.
Now, admittedly, the Saab 2000 is not the same as the 340. We are much faster. But the fact is that on short segments the few knots difference does not change the block to block time very much.
Our cabin is more spacious than an Embraer 145.
There are 3 places where I see an advantage for a small jet:
1. No vibrations. Even though the Saab has a low vibration level for a prop plane it is still more than a jet. As a pilot, it creates a higher level of fatigue.
2. Over longer segments they are faster, though not as much as some people think, since a large portion of the block-block time is spent rolling on the ground. The actual time in the air is not as different as most people think, especially on short flights.
3. But the real advantage is that they can fly higher. Our Saab is certified to FL310 and we used to fly that high but now with RVSM in place in Europe our company did not certify us for that and we are limited to FL280. This is not bad at all except that occasionally we are a bit closer to the "weather". The Embraers in our fleet can fly to FL370 and this 9000 extra feet does get them above more clouds.
Other than these three things I find no real advantage of a jet over a prop. And we have some real advantages, like the ability to operate in and out of some fields the jets can only dream about...