The first one on the left is a FREE swimsuit pattern from Burdastyle. I've used it before and my advice would be to make a mock-up or two because it's a short torso pattern.
The middle one would work just fine, if you don't use the dress pattern.
The third one would only work if you used the halter pattern.
These next two would work well if you converted them into one piece suits. I've used the one on the right which you can see here. I love the look of the bodice even though it's a little tedious to make.
Next, draw a perpendicular line where you want your gathering to stop. I wanted mine to go all the way to the top of my legs so that's where I drew my line.
Next, you need to straighten out your curved center front line. To do this, draw a new line from the middle of the old line to the middle of the next line. In this picture the black lines are the old lines. The red dots are the center of each old line. The blue line is the new center front line.swimsuit construction.