I'm not good enough with astronomy and the diurnal/nocturnal divisions that can be used in these house systems to really give a detailed answer.

However the Placidus is undoubtedly the most popular house system used at the moment for natal astrology.
Arguably a lot of people choose Koch for horary.

The reality is you can use whatever one you want. My own chart is split up differently in my profile. I've used Placidus, Whole, Equal and Koch and you can see the differences in them.

Use whatever house system you think describes you best in your own chart.

"Isn't changing the houses like totally changing everything? "

nope. The houses just show areas that the planets effect. In some ways the planets and houses describe your temperament and the house describes where you use that temperament.

Mercury in Taurus may think a lot slower and methodically than Mercury in Gemini. Mercury in 4th house thinks about the roots, the past, the father etc - the where NOT the how.

The house systems just apply a different lens for viewing the horoscope.

Use Cartesian or Regiomontanus for all.

Both are invalid as they do not confirm to any decent mathematical laws. why use them?

Campanus was found to work.

The house systems added to chaos in the past 500 years, since an already un-precessed system suffered houses. There were astrologies without houses, and those are by far the best. astrologers never needed houses. In 5 minutes you know when you marry, go to work, have baby and die, no need or houses.

The house system has done one major damage: it does not determine the ascendant. Once ther was observation, an initiate would gaze the east in second attention, what the Greeks called HOROSKOPEIN, comes from Hoor at the horizon, ok. Today you do not gaze at anything.

The Cartesian house system is compatible with any old culture, also it calculates horoscopes for births and horary in spacecraft.

koch and placidus are useless for locations beyond 66 degrees latitude

All i know about the Placidus system is that it is based on a time division, so the houses are each kind of like a 2 hour division. This would seem to me to make sense if you had a horoscope for dawn and wanted to map out your day, but not for anything else. I know nothing about how Koch is calculated but heard it became popular because it was easy for non-mathematicians to calculate.
Donald Bradley did a massive but arcane study on Jupiter positions related to rainfall in the US, in which he found Jupiter on the angles correlated with excess rainfall. He used a number of different chart positions to try and find a valid mid point between the angles where rainfall was at his lowest, and the one which worked used the same calculation method as the Campanus system. This has been taken by many as a validation of the Campanus system. Unfortunately though Campanus is one of the worst for breaking down at high northern and southern latitudes where it looks far from pretty.

Ed Falis wrote a great article on house systems a few years back which I put on another Tribe thread some time ago. Check out astronuts.tribe.net/thread/9...348460c53 part of the way down for Ed's article, although the whole thread is interesting.

Here's another little piece I like from an author I greatly respect:

What House System should I use?
Bernadette Brady
“Your Choice - No wrong or right house system
For any astrologer their preferred house system is a personal choice, but you should never just use a house system blindly. If you are devoted to one particular system, study it and ask yourself: “Why do I like it, what is it showing me which is different to other house systems?” If you answer is simply because it “works”, then I suggest that you do a little more exploring.

Also you can see that there is no "wrong or right" house system. You should choose your house system depending on the client's needs. I use Placidus generally (although I like Alcabitius myself) because I do predictive work (which is time based) and most people live in a time-based world. However, when the need arises I will use Campanus for looking for that lost object (space question) or working with a space-based person. “