For quick screenshot selection and saving to RAM I use the built-in functionality in my multiple-clipboard app, Copy 'Em Paste.
If I want to keep selecting the multiple sections of a webpage at the same location (eg screenshotting from a carousel listing) I use the ‘last selection’ option in Snap N Drag Pro. One really nice feature in Snap N Drag Pro is the ability to choose a resize option (75%, 50%, 25%) when dragging a screenshot from the app’s library to the desktop or another app; I’ll use that to send smaller versions of screenshots via iMessage or email. Snap N Drag Pro also lets you drag-export in a number of formats by pop-up selection (png, tiff, gif, and jpeg in your choice of low/med/high quality). It also allows for some basic annotations (boxes, arrows, text).
If I want to share a screenshot via link I’ll use my Droplr Pro account, and can set the screenshot to auto-delete after x number of days. If I use Snap N Drag Pro for my screenshot, I can just drag the screenshot from the SND library to the Droplr menubar to upload it.