Standard: betulifolia, calleryana, ussuriensis
Seedlings from the species Pyrus betulifolia (zone 5) and Pyrus calleryana (zone 5-6) are frequently used as a high vigor rootstock for pears, and they are similar in that they are fairly tolerant of soils that are quite heavy, wet, or dry. Betulifolia, however, has the advantage when it comes to drought, and calleryana has the advantage when it comes to excess moisture. Betulifolia also tolerates saline soil quite well, but neither of them perform better than Pyrus communis (the European pear) in alkaline soil.
Resistance to fireblight can vary quite significantly for calleryana, and it is implied that the same is true for betulifolia, but not necessarily to the same extent. There is also quite a bit of variation when it comes to resistance to pear decline, but betulifolia is, overall, considered to be more resistant, thus making it more appropriate for use with European pears. However, both rootstocks are highly vigorous and will likely cause most varieties to take a very long time to produce (sometimes over a decade), with betulifolia being worse in this regard.
As for compatibility, betulifolia seemingly has the edge. I do not recall seeing any complaints about it, but I have heard of compatibility issues with European pears and, even more so, Japanese pears when they are grafted to some calleryana seedlings. Betulifolia, on the other hand, makes an excellent rootstock for Japanese pears, since the latter is naturally precocious and dwarfing, so it has the advantage here as well.
In short, if you are in zone 5 or higher, and you are looking for a vigorous rootstock for a Japanese pear (Pyrus pyrifolia), then you should use betulifolia. For European pears, you are better off with an OHxF rootstock (Old Home x Farmingdale), since they can dramatically shorten the amount of time you have to wait before they produce, but if your soil conditions are quite harsh, especially when it comes to high density or excess moisture, then you might want to prioritize betulifolia. It is difficult for me to recommend calleryana for anything, even if your soil is occasionally saturated, because it is extremely invasive in some regions and, as I have mentioned, it has a few other disadvantages compared to betulifolia.
Pyrus ussuriensis seedlings, also referred to as the Harbin pear, are a cold hardy and (a more consistently) fireblight resistant alternative to betulifolia, calleryana, and communis, but it is best used as a rootstock for Asian pears. When European pears are grafted to it, pear decline can kill the tree very quickly, but this disease can be rare in some regions and it is only spread by the pear psylla insect. I am not sure if ussuriensis is as thorny or if it suckers as much as the other Asian species mentioned above, and I am under the impression that it requires well-drained soil. It’s quite difficult to find reliable information about this species, even though some people continue to prioritize its use for European pears (and, more appropriately, their hybrids), since it happens to be the most cold hardy rootstock available (zone 2 or 3).
Semi-Vigorous: OHxF 97
OHxF 97 (zone 4) is resistant to fireblight and pear decline, and since it belongs the species Pyrus communis and grows to a near standard size, it should be quite drought tolerant as well. However, the main advantage of using this rootstock instead of a seedling is that, in-spite of its vigor, it is somewhat precocious, but this species, especially when it comes to less vigorous selections, may not perform well in heavy or saturated soils. OHxF 97 is frequently used for Asian pears as well, but it can be fairly dwarfing with them and a more vigorous rootstock is sometimes preferred.
Semi-Dwarfing: OHxF 87, OHxF 333, Quince Province BA 29C
OHxF 87 (zone 4) is resistant to fireblight and pear decline. It is precocious, well anchored, and, perhaps, the most yield efficient rootstock for European pears that is widely available. Asian pears generally grow too slow on this rootstock, as well as on those with similar or less vigor, so they should probably not be paired together. OHxF 333 is sometimes sold as an alternative with similar vigor, and it may be resistant to collar rot and woolly pear aphid as well. I am not entirely sure if these are legitimate advantages though, since I have never seen any implication (other than omission) that OHxF 87 or OHxF 97 are susceptible to these afflictions, but there are a few trials that demonstrate its disadvantages. OHxF 333 is not as precocious or as productive as OHxF 87, and it has a habit of producing smaller fruit than the other rootstocks mentioned here when the same variety is compared.
Quince Province BA 29C (zone 5b), also known as 'Province Quince', is the only quince rootstock that seems to be readily available in North America (at the time this was written), and in most cases, the problems that come with using this species, in comparison to Pyrus communis, is probably not worth it for most people, because BA29C may not produce trees that are significantly smaller or more yield efficient than OHxF 87.
Some of the problems that come with using quince include susceptibility to fireblight, weaker anchorage, more suckering, less tolerance to dry soil, alkaline soil, and low temperatures, and incompatibility with a number of varieties, meaning that an interstem (e.g. Comice) would be necessary for certain combinations. Conversely, quince supposedly tolerates clay soil better than communis, which may make it worth experimenting with if you do not wish to rely entirely on standard rootstock. Quince is somewhat resistant to pear decline as well, but in this regard, OHxF rootstocks are going to be superior.
Amelanchier (juneberry) can, at times, be used as an extremely precocious, dwarfing rootstock for European pears, but improved selections are not available to the public yet. Unfortunately, they are similar to quince in that they are known for having compatibility issues with a number of varieties, but Comice may be used as an interstem for Amelanchier as well, since it has worked for at least a few of those that have been trialed. Amelanchier has a couple of other advantages over quince, with the most important being that they are hardy down to zone 3, resistant to fireblight and pear decline, and are more tolerant of alkaline soil, although these traits may be more or less true depending on the species that is used.
It seems that Almelanchier can be split into two groups when it comes to the height of which they generally grow: over 20ft and under 10ft. I am not sure which species are preferred when it comes to grafting pears, but I found one short term trial that involved Almelanchier alnifolia, canadensis, and lamarckii. I also see home-growers experiment with alnifolia on occasion, implying that it is fairly compatible. If these are the species that are generally used, then those that can grow to over 20ft in height may be required.
Related: Pear Varieties