Here the standard still is St. Julien A. It has very good compatibility to all E.plums and is somewhat dwarfing (70% vigor vs. seedling). It is used also for peaches and apricots. But there are more and more voices that suspect problems when using it for peaches and apricots. With peaches and apricots winter tree losses are higher on St. Julien A than peaches and apricots on peach seedling or apricot seedling. Therefore I dont use plum rootstock anymore for my peaches and apricots. Plus St. Julien A is somewhat demanding in regards of the soil quality. It doesn’t like sandy and dry soils.
Another St. Julien plum for rootstock is St. Julien GF 655/2. That one is suckering and I wouldn’t choose it over St. Julien A.
In newer field tests another E.plum rootstock proofed to be superior to St. Julien A in regards of survivability. Its called Wangenheim (propagated by seed) or WaVit (propagated by tissue culture). Especially WaVit has very good compatibility to all E.plum and even to apricot. Its only drawback might be it even is a little more dwarfing than St. Julien A.
Myro is another good rootstock for E.plums with high vigor. It has compatibility issues with some varieties of E.plums (eg. many Gages) and with some varieties of apricot. There are selections of Myro with better compatibility, Myro 29C might be one of them. I have no experience with it.
Brompton is another plum rootstock (prunus domestica) for E.plums and peaches with high vigor.
An old-timers choice for E.plums are seedlings of Green Gage. This rootstock has the vigor of a seedling but is trouble free as far as I know.
And then there are prunus tomentosa. They can be propagated from seed and are very much dwarfing. There are hybrids from prunus tomentosa as a more recent rootstock for E.plum, eg. Weito Klon 226. I don’t know much about them. I sowed some to test them as a rootstock.