This may depend on what type of grass it is. Grasses like Bermuda aren't killed by rototilling.

If you do decide to remove the sod, you can pile it up behind a bush, wet it thoroughly, then cover it with black plastic for a couple of months till the grass dies. Then you can re-use that soil in another part of the yard (though it'll be better if you wait a few more months for the dead grass to disintegrate -- the compost pile is a good place for this).

This spring I'm enlarging a bed in my lawn. Currently the new area is covered with heavy black plastic (10' x 25'; from the hardware part of Walmart rather than the garden center), held down with garden staples (which can be found at Lowe's with the landscape fabric). The plastic has been in place for just over two months, and that grass is well and truly cooked! (There may be some bits of Bermuda with some life left in them, but most of that is dead also.)

Sometime soon I'll remove the plastic and the landscaper will rototill it. I'll sift out the clumps of dead grass as I plant -- but that's more for aesthetics and ease of planting. When I did the first part of the bed, I buried bits of the dead sod in the holes where I planted -- extra humus deeper in the soil.

There is no single best way to prepare a bed. I use black plastic, but some people use clear plastic. Others just pile things on to make what's known as a "lasagna bed." I've done lasagna gardening, but I've never tried to kill grass that way. Some use weedkiller; if you do, just be sure you know if it will have an effect on your plantings.

The verb for what a rototiller does is "rototilling." Here people mostly say "tiller" and "tilling," but we're rather rural. However, at times it's useful to differentiate between the tractor (which is much more efficient at breaking up the sod for the large rectangle of the veggie garden) and the rototiller (which is much better at negotiating the smaller spaces and curves of the new flower bed).

Yes, you will lose soil by removing the sod -- it's hard to avoid. But most turf grasses are rather persistant and just tilling them under will only create serious weedy problems down the road. If you have the time, removing the sod and laying it root side up can be effective. The exposure to the air dries out and kills the roots and the topgrowth is effectively smothered (may not work well with the Bermuda grass, as stated). But this does not happen immediately. You can speed up the planting process by piling on soil or compost over the top of the turned sod, depending on how much soil you are adding and if you want the beds mounded or raised.

IME, the "best" planting bed is one that has as much of the existing weeds or other growth (including lawn) as possible thoroughly and completely removed or killed before amending and planting. How you get to that point is up to you :-)