I recently posted a fairly positive comparison of Stash vs Instapaper. There's one point that has changed significantly since that post was made:
Stash is no longer a free service.
That's right: After I just got done posting about how Stash is pretty rough around the edges and needs some work (though shows a lot of promise), they sent an email to their existing users giving them 10 days to decide to upgrade to a paid plan.
The rate is reasonable and simple--$3/month, no options to choose from. Additionally, existing testers, if they subscribe within their 10 day limit, will become premium users that get a few bonus features, and a discounted rate of $2/month.
The real question boils down to, for $2 or $3 per month, is Stash still a viable alternative to the excellent (and free) Instapaper?
This does change my recommendation slightly. The barrier to entry for using Stash is now larger, and Instapaper has one more serious point in its favor. So if you're perfectly happy with Instapaper and don't particularly need any of the features Stash is offering, you've got one more question to ask yourself: Is it worth spending money to try out another service that's known to have some quirks and a poor Android experience?
I, for one, have decided to upgrade and fork over $2/month. For a total of $24/year, I'm already seeing some benefits to my workflow in using Stash, mainly from the incredibly useful browser extension that lets me categorize and set tags and reminders right away when I add something to my stash.
Your mileage may vary. I will likely continue to share my experiences with Stash as the service evolves, and will report back if I decide to switch to another service as well.