tights or bibtights without chamois are cheaper, sometimes as much as $40 cheaper. This way, you can don't have to invest in a more expensive pair of clothing with chamois that you won't ever use in the summer. The seat/chamois/pad is the main part of the garment that you need washed, you don't have to wash the tights that don't have chamois as often. You can just buy one pair and use them with all your regular shorts/bibs.
I like bibs better. They don't have a waist band that's putting pressure around your midsection. This feels much better. If you have regular shorts with chamois and waistband, and you get a pair of tights with waistband, you now have TWO wastebands constricting your stomach. Winter bibtights cover more of your front and rear upper area than shorts, not just with the straps but along the lower back and stomach.
In the summer, bibshorts also feel better because you don't have sweat collecting around, and soaking into the waistband. Your midsection, both front and back, has an open channel for air to circulate freely, keeping you cooler.
I'd recommend Santini bibtights. You can get a pair here
. I have another model, and have a couple pair of their regular summer bibs. They are more durable than normal, and more comfortable than others I've tried like Castelli, Assos, and Voler.