Is the container something like these? I think wash tubs are/were galvanized? The Persian shield has come back for the past few years, Coleus re-added each spring. If you put Tradescantia zebrina at the base, you'd have a perennial combo, creeping around the sides.
This one's on the other side of the house. Nothing perennial going on in there but some Oxalis crassipes bulbs (currently dormant, handy arrangement.) I like playing with it each spring, seeing how many things I can cram in and seeing what it can do before frost comes.
If this was a general question about preference, I'd vote shade! I mean I'm about sick of any pot out in the sun at this point, to the point where I just don't want petunias if they are boring in a lump in the ground, or marigolds or dwarf zinnias or snapdragons if they are too short to see in an available ground spot. It's raining way too much, so now everything's crammed on the porch anyway, to avoid the bulk of the water. When the sun is blasting, it makes pots really hot down through the roots, so I think it's hard to find a happy medium. The rain has only added the element of trying to move pots at this point, the "baking too hot" thing's always been an issue. Love the look of pots on the porch steps, but the concrete get so hot one can't walk on them with bare feet. So you know the pot's dry, it feels lighter, so you water often, the soil is well-drained, but the plants still don't do as great.
After decades of watching potted plants do crappy in non-stop sun, whether I water them a lot or a little, I don't think I'm going to put myself through it next year. I'll still have a few of these pots, but I'm going to sit them in flower beds, where they'll stay a bit cooler, pots shaded by other plants, and the wicking action of contact with the ground makes for so much better drainage. Also not going for divas just because of some short-lived flowers, but more stalwart entities like Pentas, Angelonia and interesting fast-growing succulents that don't need large, bright to make a statement. Those don't have anything to offer hummingbirds anyway usually. The Cannas I put next to the steps should be "leaning up" all of the extra space anyway, and are enjoyable to hummers. Hmmph, so there! LOL, like a rant, but I'm really just babbling with a smile, enjoying every minute. If there was no such decisions to make each year, what in the world would there be to talk about? And if it always went great, new ideas would be much less... numerous and interesting.
Does anyone else have the general frustration with pots out in the sun (excess rain notwithstanding?) I think if I had something really big like a whiskey barrel, (but not metal as mentioned regarding the container that started this discussion,) it would probably do a lot better. Don't have a garden budget for something like that, but if something free (that's not too fugly) presents itself, I'd love to experiment. Metal gets too hot to touch out in the sun (remember the slide when you were a kid - OW!,) just like a black pot. You can feel it's much hotter than the already hot air. I think avoiding using such materials/pots when one knows it's going in full sun is probably prudent. Full sun doesn't mean 120-degree roots, unless you're talking desert plants, AFAIK it's overwhelming to a lot of plants. Then, if one has their heart set on something being in the sun, there's always a coat of paint, or surrounding with smaller pots, you know, a pot garden.
Wonder can I teach the dogs to dial 911 
and wear gloves
and pants with a pocket for the "snake charmer" 
