Here’s what I’d say depending on the situation. All of these will be going off of one popular species that is notoriously difficult, an Achilles Tang. However the bits I’m about to say can generally be put into any fish no matter the difficulty (although some parts for example the sizes I mention in the first bit are variable from fish to fish). These thoughts are coming from someone who has worked with the live stock part of an LFS (Ordering in and looking after certain fish) as well as what I look for when buying my own personal fish.
1 - Shipping/Establishing to captivity;
Ideally in this situation, you want fish that aren’t too large but also aren’t too small. If it’s a fish that’s between 3-5 inches this is ideal. These are slightly more mature fish that won’t suffer as badly from a new environment but also these fish aren’t on a fully established wild diet but they have a diet we can use to our advantage so they’re quite easily moved onto frozen/prepared. Now, if you have a 1-2 inch fish or smaller, you risk them being 10x more fragile to diseases brought on by stress from a new environment. You also risk a starving fish that eats a different diet to the more mature specimens so we may not be able to sustain this diet fully. You may be thinking ‘what if it’s a fish larger than 5 inches’ well, generally these are on a diet that is hard to move them from. Generally with tangs this diet is algae which is easier to ween them onto a second diet however with some other fish like butterflies which tend to eat specific coral polyps we can’t quite ween them off of this diet as easily.
2 - Lifespan
This is one situation where it really varies from fish to fish. Generally speaking the fish we own in captivity live for 25-30 years or more with the obvious differences being Wrasses, Gobies, Blennies ect. So, generally you’ll want a smaller specimen the youngest ones are usually in the 1-3 inch range. Now this comes with its own issues (See above) however on a Lifespan situation, you ideally want this. Now, I’m aware some fish will be max size yet have 10-15 years on their life still but I’m sure you’d want to keep this fish for as long as possible. If this is the case, then you really want a 1-3 inch fish. At max id say 5-6 inches however in that range, we’re talking about a fish that’s likely to be half way through its lifespan. 7+ inches is generally a fish that won’t last too long (again I’m talking about an Achilles tang so this will range depending on the species of fish).
3 - Pricing
Pricing is on some fish you’ll get a smaller specimen for less however on other fish you’ll get more. Again, I’ll be basing off of an Achilles Tang in which the younger the specimen I’ve found the pricier they get. This is unusual but makes sense as this is a fish which is notoriously difficult as a more mature specimen but 1-2 inch specimens are even harder to get through shipping and then establishing to captivity. However on other fish, for example Clownfish, these are pricier the larger they get due to them being so common as young specimens to the point finding a fully grown one is rather hard.
I hope this answers your question in enough detail (I could’ve gone into more detail but that would’ve ended up in me rambling about Wrasses).
