2800 mAh will give you a slightly longer time between charges. 3.8V is a marketing gimmick - lithium batteries are 3.7 volts. (That's determined at the sub-atomic level, the manufacturer can't change it and "make" a 3.8 volt lithium battery.)
If they're from the same company, and the same price, I'd go with the 2800mAh one. If not, I'd go with the company with the better reputation. (I always stick with Anker and Hyperion, and my batteries last longer than the phones they're in. The secret is to NEVER let the battery drop below 40$, except for the first 3 charge cycles - then fully charge, leave the charger in for at least another 30 minutes, then use until the phone tells you to charge it. Do it twice more.)
My over-10-year-old V551 batteries still give me about 95% capacity. The phone even has a camera. (That was new back then.) By the time the batteries die, someone else will be killing them. I'm 72, I won't live long enough to see them die.