there are probably about as many panzanella recipes as there are households in tuscany, because it's essentially an old bread salad (stale and hard bread works best here) with tomatoes and whatever other vegetables need using up. it's a "leftovers" dish so i feel especially free to customize it, and i have. for instance, i like this salad to be especially tart so i add olives in addition to the capers. i also like to make the croutons for this dish very dry, so i make mine in the oven instead of over the stove. and often when i have the oven going, i use it as an excuse to roast some garlic, so i throw some of that into this salad too.
but despite taking liberties with this dish, my list of preferences is long too. i like the tomatoes to be the star vegetable, so i don't add cucumbers, peppers or any of the other vegetables commonly used in this salad. and i think a thin, red wine vinaigrette is perfect for this, but you might like it better with white vinegar or even sweeter balsamic. don't let my pickiness when it comes to this salad hold you back. this is just my favourite way to make panzanella. it might be james' too. he told me about 3 times how much he liked this when i made it a couple of weeks ago, which is rare commentary–he usually needs to be prompted for feedback (too busy eating, he says…)
one tip i think that's worth trying is to let the sliced shallots mellow out in the vinaigrette while you get on with the rest of the prep. it's a tip i learned from my mom. having them sit in vinegar takes the edge off the shallots and it also imparts more flavour to the dressing. so i'd say try that, but use the rest of the recipe that follows as a jumping off point to make your own favourite panzanella.