Whatever these "old DOS games" require.

That is just it. I am not familiar with old DOS games that ran on a 8088.
I am thinking about an IBM Color Monitor maybe a 5153
And an old IBM computer. Maybe a 5160 or 5170 or 5150 or XT
Which one would work best and why ?

If you want it for the oldest games that were designed to run on a 4.77 Mhz 8088 then you should just get a 5150 and 5153 monitor. If you are not just talking about games designed to be played at 4.77 Mhz then you may want to consider a 5170 with an EGA or VGA card and 640k expanded ram. I think since you already have those other machines you are looking only for the 8088.

You can go for clones but I find IBMs build quality to be consistently superb from that time period.

Very early DOS titles tend to be quite speed sensitive and will only run correctly on a 4.77 MHz PC.

There are a number of good 100 % IBM compatible XT clones that you can also look at and that might be easier to source than an original IBM PC (model 5150 or 5160).

Many later XT clones were actually Turbo XT's since they utilised an 8 MHz or sometimes even a 10 MHz Intel (or AMD) CPU that could be slowed down to run at 4.77 MHz.
Just try and avoid any clones that utilises an NEC V20 CPU, since those CPU's sometimes tend to run slightly faster than the original Intel/AMD CPU at the same clock speed.

For this era type of PC, a CGA (and an MDA/Hercules) card will be the most suitable.

You don't necessarily need an original 5151 and/or 5153 monitor - any clone should suffice (once again, since they might be easier to source).