Depends on the home, trim, etc. Do you have an installer already? Shouldn't this be a question for that person to review with you?

You prefer to paint the wood exterior trim? I would mostly defer to outside set as that preserves the interior trim and spares it from possible damage.

This may be regional so treat it accordingly, but in my area an inside install is highly unprofessional in the majority of circumstances and reserved for DIY'ers or laborers masquerading as window installers. The fact that your home is more than 80 years old means that lead safe renovations procedures will be needed and the extent of those is night and day on an interior vs exterior install as well. Much less invasive on exterior install.

Thanks, @Windows on Washington Ltd. I am checking to have an educated discussion with my installer. What I am reading online is that that vast majority of people say it does not make a huge difference (other than limiting potential damage to trim). That said, a handful of people say that, in colder climates, everything else equal, an inside installation might offer a better seal. I'm not sure whether that info is accurate.

I would prefer to paint the wood exterior trim and not use aluminum capping.

In the geographical area you service, for an 80-year-old brick house with thick brickmould, what is the most common method? Thanks again.

Thanks, @HomeSealed Exteriors, LLC. All you mentioned makes perfect sense, although I was not aware that professionals clearly prefer outside installation of insert/pocket units. Other than lead paint related issues about disturbing the interior trim, is there a clear advantage of an outside installation in terms of seal and water/air tightness? Thanks.

I forgot to add: Installation instructions for Marvin Ultimate says that, for double hung units, interior or exterior is fine; however, for picture units and transoms, interior install is preferred (page 3 of https://www3.marvin.com/WebDoc/Clad%20Insert%20Double%20Hung%20Next%20Generation%202_0%20Installation%20Instruction%2019915904.pdf). In my case, all my units will be double hung, but I am curious to know whether this is consistent with the notion that, everything else equal, exterior install is much better...

Inside installation does NOT, on its own, allow for a better seal. So you can eliminate that non fact as a decider.

Either are just as watertight and to be frank, you won't have any issues if the person is competent either way.

The ability to leave the interior trim untouhced and the sizable advantage in the lead safe renovation process are the two main benefits to exterior install. As WoW stated, there is no major functional difference in sealing or anything of that nature, its more reflective of the skill and experience of the installer (again in most cases, not all). Most non-professionals don't have the knowledge, skills, or equipment to do an exterior installation.