mounting antenna on a house which is better x-polarized or linear polarized or doesnt matter?
Any reason specifically to use an omni? I tend to favour directional antennas on things that don’t move as you can aim them right at whatever tower will give you the best service, hint it may not always be the closest one 
X-Pol can help create more tx/rx diversity, generally speaking I would use an X-Pol antenna over a linear polarised one these days, chances are the cell sites are X-Pol too for the same reasons these days.
Oder sites or very rural sites may still be vertical polarised antennas – this depends on country to country and operator to operator though.
x-polarized is better in my experience.
which way do you point an omni x-polarized? they are rectangular.
which one from here would u recommend: https://poynting.tech/antennas/?filtering=1&pa_mimo=2x2-mimo&paged=1&pa_polarisation=x-polarised
open to other suggestions as well
Well an omni generally doesn’t really care, mount it on the pole as the bracket would permit and you are probably good to go.
As for “what to buy” the Poynting stuff is pretty good, I would go for the one with the widest frequency support, you may also consider installing a 4 element MIMO antenna even if you only need 2 elements at the moment as that way you are covered for the future if you decide to upgrade your modem - most 5G modems will require 4 elements (or potentially more in the future!).
Other options:
Peplink’s own antennas are pretty good, we have been having very good results with the mobility series ones, they are a bit more costly though than the Poynting.
Other brands that I use regularly are Panorama and Taoglas, both make plenty of good options and similarly priced to the Poynting.
Newly released, not personally used it yet but the specs seem decent.
Used several of these recently with good results.
Consider carefully the cable length from the router to the antenna, the rule is generally keep it as short as possible but I would typically avoid anything more than 5m/16ft if you need more it may be better to relocate the router.
You can get away with more but that is generally when using high-gain directional antennas and more chunky cable than you get with most of those antennas - something like LMR400 is a starting point for us there.
Peplink’s antennas are linear though i think?
They are, but in some respects so what - it does not mean it is a bad antenna or going to perform dramatically worse.
In some respects they are a higher gain antenna than the Poynting in some bands (read the data sheets, compare gain in the bands that you actually care about, not just the headline number given as that is typically “peak gain” not specific for a given band) and cover a slightly broader range of frequencies so you could argue they are in some aspects a technically better antenna vs the Poynting.
You asked for other options to consider so I have suggested things that I have personally used, or vendors that you could investigate who have a multitude of antennas on offer - just a case of filtering out what is useful for your specific installation.