I took a look at servint before and I would never go with them as they don't provide true VPS's, at least in my opinion. You only have one choice of OS, as far as I know it's almost completely managed for you, and they use Virtuozzo for virtualization instead of Xen.
Linode is much more open. You can choose whatever OS you want, partition your virtual drives however you want (so you could theoretically have multiple systems installed on different virtual partitions), install whatever you want and basically do whatever you want with your Linode (assuming it is legal). They also use Xen, which does a better job at isolation and makes overselling an impossibility.
Finally, they have an extensive Linode Library with thorough tutorials on how to do all sorts of stuff with your Linode, and their prices are great.
I also looked at VPS.net but decided on Linode because I had heard many good things through word-of-mouth.
The only problem I have found with them is their storage prices. The amount of storage you get for the price is cost-prohibitive if you need to host lots of data or a collection of larger files. You could use S3 or another provider for storage, but that's a real pain. That's the one thing I really found attractive about VPS.net - you could add "storage nodes" on to your VPS plan for fairly cheap.
This is the only downside of Linode. They do not offer any sort of control panel (aside from their "virtual hardware" control panel, as I call it, which lets you restart the server, install OS's, manage DNS, etc. - but no cPanel/WHM). They don't even sell licenses actually - while you could easily install cPanel you would have to purchase a license from a 3rd party first. Personally, it's not worth it to me. If I want to do something I usually just learn to do it from the command line, and phpMyAdmin handles all my MySQL needs.
I've been with ServInt for about 5 years and been very happy with their VPS packages. They *may* allow different operating systems if you ask because I moved from RedHat to CentOS about a year back on the recommendation of one of their techs. It's nice to pick up the phone any time I want and instantly be talking to someone who can help with something. They offer a lot of hand-holding and I've learned a lot from talking with the techs.
can also just recommend linode. it´s a lot of fun because theire vps´s are very close to a root-server. eaven own compiled distros are working fine there. sure the small ammount of gb per plan is a bit downside but for most users may not that important.
i own several root and vps-servers (mostly in germany) but only a few are offering xen-virtualized vps and with less futures.