Nearly a year ago when I last upgraded my printer beds, I switched to steel. This has two advantages: first the z probe registers much sooner (thus higher/further from the bed), this allows me to raise up the probe so it's less likely to hit stray filament blobs or prints. Plus, I can place thicker print surfaces on the bed without gouging the hotend nozzle into them.
Here's a pic of the 305x150mm bed on my older Simple:

The second advantage of the steel bed is that I can use magnets to attach easily removable print surfaces. When a print completes, I simply pull the magnet off the bed, & then bend the magnetic sheet and the print peels right off; no putty knife required. For a long time I printed both PETG & TPU directly on 0.06" thick vinyl coated flexible magnets:

I purchased 24"x24" sheets from McMaster Carr for about $8 a piece, & then cut them into 6"x6" & 6" x 12" sections.

Here are several prints in progress:


Here's a print that utilized the whole bed:

The only down side to the vinyl coating, is that eventually it would wear out & peel off with some of the prints:

I've been trying other surfaces attached to magnetic adhesive backed strips:
Kapton sheets work really well, but are a bit pricey:

These styrene sheets are fairly cheap & work pretty well:

However, the least expensive surface I've found so far is "Metalized Polyester" film. $10 for a 27" x 12 foot roll at McMaster. It performs remarkably similar to Kapton sheets at a fraction of the cost:

I'll update this thread as I try other surfaces. I also have a sheet of garolite which supposedly works well for nylon, which I hope to try when I get the eSun nylon I just ordered.