Which zoom lens/lenses (24-105, 24-240, 70-200 etc)?

I'm unsure I can answer your question, but maybe I can give you some information. I have made comments inline below.

LennyLevino wrote:

I am looking for a nice zoom lens or two to complete my travel and hiking kit. I have a Canon R6 and the following RF lenses currently: 15-30mm STM, 16mm STM, 50mm STM, 85mm STM.

I am mainly debating between the RF 24-240mm f/4.5-6.3 IS USM, vs RF 24-105mm f/4-7.1 STM + RF 100-400mm f/5.6-8 IS USM. Locally, the price for either kit would be about the same ($900).

I generally like the RF 24-240 as a walk-around do-everything lens. The much better and faster focusing is a big advantage over the 24-105 STM.  The RF24-240 is very sharp in the center, even wide open but does suffer in the corners, particularly at either end of the zoom range. In most normal shooting, you probably will not notice the difference.

The RF24-240 is the first RF lens I bought, and I still use it even though I have gone on to buy over $15,000 of RF lenses. It is the most "fun" lens I have, but I would say the RF100-400 is a better "value" based on image quality. I would have kicked to the curb the RF24-105 STM.

The benefits of the 24-240mm is I would have only one lens that could do pretty much all I need. But with the two lens setup would gain almost twice the focal length. I'm guessing telephoto range (around 200mm+) would be better on the RF 100-400 as well.

Yes, the RF 100-400 has visibly (on close inspection) better image quality over its entire range that overlaps the RF24-240. I bought the 100-400 as a "long travel lens" as I already had the RF100-500L (and if I have room/weight, I will take the RF100-500 mostly for the extra range and edge in image quality).

A third option is to get the 70-200mm f/4L. It could probably become more of a hassle though as I can't just walk outside with one lens attached to the camera and expect to capture most of what I want/need.

So here are the kits I could do and fit in my camera bag, combining with the lenses I already own:

Kit #1 (24-105 + 100-400mm):

1. RF 15-30mm f/4.5-6.3 (already own)
2. RF 24-105mm f/4-7.1 ($249)
3. RF 100-400mm f/5.6-8 ($599)

Pros: Long reach (up to 400mm), higher quality on the telephoto shots. In situations here I might not need more than 100mm, the 24-105mm is considerably more light and compact versus the 24-240.
Cons: One extra lens to carry (in most cases), and the 100-400mm is quite large and heavy. Also IQ on the 24-105mm is questionable compared to the 24-240. But would like to hear some experiences.

I would suggest saving your money for a better mid-range zoom or spending more on the RF24-240. As said above, the RF100-400, I think, is the best "value" based on price and image quality that I have seen in any RF lens. It compares favorably in image quality, focus speed, and IS to L lenses (It probably would have been considered an L lens 10 years ago).

Overall, I would suggest buying fewer but better lenses.

Kit #2 (24-240mm):

1. RF 15-30mm f/4.5-6.3 (already own)
2. RF 24-240mm f/4.5-6.3 ($899)

Pros: Less lenses to carry. Might be fine just going out with the 24-240mm alone, since I don't shoot much below 24mm anyway. I also have the RF 16mm prime that I could more easily bring along instead of the 15-30.
Cons: Less reach (240 vs 400mm), probably slightly lower IQ in the 160-240mm range. This lens is also considerably bigger and heavier (almost twice as heavy) as the 24-105mm STM. So in cases where I don't need more than 100mm, it would be more cumbersome to use the 24-240.

I like this better than getting the 24-105STM

Kit #3 (70-200mm):

1. RF 15-30mm f/4.5-6.3 (already own)
3. RF 50mm f/1.8 (already own)
4. RF 70-200mm f/4L ($1399)

I would get the RF100-400 instead of the RF70-200f4. On my last big trip, I found my RF70-200f2.8L stayed in the bag or at the hotel. I would typically pack the RF15-35, RF24-70, and RF100-500L. For my uses (others love the lens), the 70-200f4 is neither fish nor fowl, it is not a very long telephoto, and F4 is not particularly fast for indoor or portrait use. What kills both the RF70-200L lenses for me is that neither accepts a TC. As such, it kept loosing our when I only wanted to carry 3 lenses.

Pros: Highest image quality on the 70-200mm focal range. This lens is also slightly smaller and lighter than both the 24-240 and the 100-400.
Cons: No "do-it-all" lens. I would have to carry at least two lenses every time I go out. Also this kit is considerably more expensive than the others.