Each machine has its own advantages, as mentioned earlier the Envision is much faster and can home when paired with a printer.
If you're working with Lexedge the HS 15 plus hands down wins because of the tangential blade. Polycarbonates with a swivel blade just frankly seems preposterous.
If you're working with small circles (especially on thicker materials) the Envision fails to meet expectations; often small circles will become oval or non-concentric. If you demand high tolerances on small circles (0.375" or smaller) you can circumvent the issue with a GSX or GS 15 Plus plotter via swivel blade and plot very slowly.
The Plotter Doctor is a good source if you need parts or repairs on the HS series plotters; Gerber discontinued service several years ago on the HS series. Think the control pad will get you with some sticker shock if it breaks.