Do I need my lap band emptied before I get a revision? Is there a preference between sleeve and bypass after lap band?

Hello, I hope you are well. After a lap band it would be most appropiate a conversion to gastric sleeve. Although a decision between a sleeve and a bypass depends on various factors that you do not mention, a gastric sleeve is probably your best choice.

You really don’t need to empty the band if you have no complications.
The surgery can be done safely, as a one stage operation, where the band is removed at the same time as the revision.
Both options of Sleeve Gastrectomy and Gastric Bypass are good, but most surgeons including me recommend the Sleeve as it’s less invasive.

It doesn't look like you will need the Lap Band emptied unless you have some sort of obstruction. Normally, the lap band is removed during the first part of the revision surgery. 
You also asked which revision surgery is best for you (sleeve or bypass). It would depend on your current BMI. If you have a BMI higher than 50 then a bypass would typically be the best option. Under 50 BMI you could go either way and it depends a lot on you current medical condition and weight loss goals. Talk to a bariatric doctor in order to get a better idea of your options. 

If you are symptomatic with obstruction; GERD, vomiting, difficulty swallowing... then I would empty the band first.  If you are doing fine and have no difficulty eating, then I wouldn't bother to empty the band.My preferred operation is sleeve gastrectomy.  It has similar weight loss as gastric bypass, but a much lower complication rate.  If you are paying out-of-pocket, total cost with me, including hospital and anesthesia, would be about $13,000 for the conversion.Regarding one or two stage; I always do the conversion in one stage unless the band has eroded into the stomach.

Great question.
Best answered by your surgeon. 
Some would actually have 2 stage procedure. First - remove lap band.
Allow any swelling to go away. Then- bring back for Sleeve or Bypass.
We would at least decompress the lap band first.
Also, consider ESG. Endoscopic Sleeve Gastrectomy. Less maintaince the Band.

Good Luck