The genus Aechmea includes the greatest amount of cold hardy species, such as the popular "Matchstick Bromeliads", Aechmea Gamosepala and Aechmea Cylindrata, which get my picks for time proven toughness. "Blue Cones" is pictured to the left, which is a hybrid of cylindrata.
These two and their hybrids are quite similar, but the majority of them feature clumping and low growing rosettes of foliage with a blue and pink flower spike with bracts resembling matchsticks. Other tough ones are A. apocalyptica, A. recurvata, A. winkleri, A. calyculata, A. caudata, A kertesziae, A. distichantha and A. Nudicaulis, though there are many more.
They can be grown in well draining soil as an accent, groundcover or focal point, but its in the trees as epiphytes that they really look impressive. I recommend placing offsets in palm trees like windmills and letting them form clumps at eye level.
There are a multitude of cold hardy Billbergia Hybrids with drastically different flowers and forms. Many of the toughest ones color nicely in sun, often with pink spotted foliage! Billbergia Nutans, or Queens Tears have soft and wavy green leaves that drape down nicely, especially when planted as an epiphyte. Still others, like Billbergia Pyramidalis 'Striata' or 'kyoto' have variegated foliage with yellow stripes or white margins, respectively.
You can usually identify Billbergias by their slender form and short lived but magnificent flowers. Pyramidalis Hybrids are borderline for me in 9a, so make sure to give them protection.
These are succulent terrestrials with amazing spiky, tightly clustered rosettes. Though there are other cold hardy terrestrials like Puya and Bromelia, Dyckia get my pick for the average home gardener for their tightly clumping nature and smaller size. Many like "Cherry Coke" and "Red Planet" have deep burgundy leaves, while others are green, bronze or jet black. The contrasting white spines look menacing yet very ornate, and actually point forward and backward! To the left is a shot of "cherry coke" flowering at the UNF campus.
Grown mostly for their architectural foliage, Neoregelias have an astounding variety of hybrids to choose from, with many of the leathery ones suitable for colder winters. Neoregelia Spectabilis is a common passalong plant with pink "fingernails at the tips of the leaves, and is quite hardy in sun or frost. Neoregelias will sustain damage in the coldest winters, but they usually recover quickly. There is a clump of Neoregelia "Betty Head" growing in an old oak tree despite the recent cold winters. It took a big hit this year, but this was with no protection. My recommendation for those with hard frosts is to plant them in protected places. If you want them in trees, plant stoloniferous types at the tree's base and let them climb!
When the freezes hit my local garden centers and nurseries, it was interesting to note that while the guzmanias burned to a crisp, the vrieseas got off almost scot free. Although the mother plants died, all of the pups were unharmed even though these individuals were of amazonian origin. If you're feeling a little less brave, try some of these exceptional species from Southeastern Brazil! Vriesea Philippo Coburgii, V. Vagans, V. Lubbersii, V. Corcovadensis and V. Flammea are all great choices if you get frost. My philippo coburgii was left out in the open and only received a little leaf damage! To the left is a Vriecantarea "Inferno", which is an intergeneric hybrid between Vriesea and Alcantarea. This very large hybrid is also reportedly very hardy.
(Though "the best" is definitely open for debate, I've spent the last several years researching through books, the internet, publications, anecdotal evidence and from personal experience. If you have any pertinent info be it a disagreement or a shared success, leave a comment or let me know.)
Here's a link to a post I did on cold hardy Billbergias