Swaret is very good for base packages, the stuff that comes on the slackware disk. Slackware current packages are very stable. I use a cron job that upgrades my slackware systems daily, I dont give it a minute of worry. I have given slapt-get some thought because of the veriaty of proggies you can get with apt.
I have not tried
Emerde , but if it is as good as emerge on my gentoo box, it may very well be the slackware holy grail.
Oh, only bad thing about swaret is that it keeps copies of packages in /var/swaret---- I have one machine that the partition is not very big for /var/ (I set it up before I started using swaret)---when /var gets full it crashes the machine because there no room for logs--the system doesnt like not being able to log stuff. There are many ways I could fix it.