I've been with Linode for just over 2 years now (I think my monthly bill is just north of $300, about 10 instances with them) and I'd highly recommend them. I've had maybe 4 or 5 servers down over my life as a customer, normally due to ~10 minute network issues and I once had a server go down due to the host machine and I had it back in 30 minutes.
The best thing about Linode is the support: if an issue happens they open a ticket with me and if I reply with questions / clarifications I'm replied to within a couple of minutes. Their pricing is a bit higher than elsewhere but after having shitty experiences with another company (vps.net) I decided to bite the bullet and switch and haven't regretted it since.
The billing isn't as flexible as EC2 (but then I guess they're different markets) however you get pro-rated payments to the day. So a server up for 10 days will cost 33% of the monthly cost and they refund the amount to you in account credit when you remove the server. Flexible enough that it can be helpful when you just need a server for a couple of days. Oh and their nodebalancer product is great.
I have seen complaints about one of their datacentres having some issues (Newark) but I can't comment on that as I use their London datacentre almost exclusively.
They are kind of different beasts. Linode can spin servers up and down rather quickly and you can deploy different OS's all through the online menu.
Prgmr you buy a machine send an ssh key they set it up and send you the bill. Then you get a login console at xxxxxx.prgmr.com and login and setup a user or deploy your own OS using centos recovery. But you can't create and destroy servers like linode or aws or rackspace.
I've had a couple prgmr VPSes for about a year and I'll say this: I've never had any interruptions, they are always fast when sshed into, and make good web servers. The only problem, and its kind of a big one, is that support sucks. Reseting your ssh key (which I stupidly have needed to do a couple of times) takes about 3 days. You send them an email and they respond... eventually. But you get what you pay for and its hard to ask for much service when you're paying those low prices. For the price, the servers themselves are awesome.
I'm switching to Azure because their prices are reasonable and you get the full management experience.
I've only been with Linode for a year or so after coming previously from a Mediatemple Gs plan which costs the same per month but lacks in performance. I've found Linode's support to be better than expected, I am somewhat new to administering my own server via a command line and accidentally destroyed my site and they were able to bring it back for me (a configuration issue somewhere deep when trying to setup email). I've had nothing but a great experience with Linode not-to-mention their helpful guides for installing Nginx, Memcached, Wordpress (via command line) and offer third party apps definitely helps considering I am no system administrator by any means.
I am currently hosting one major site running Wordpress on my Linode box which gets roughly 17,000 uniques per month coupled with a plethora of other domain names and blogs (about 10 other sites) they don't get as nearly as much traffic though I have running on their 512mb plan and I haven't hit any kind of resource limit in terms of CPU, space, memory or bandwidth just yet. I am pretty amazed a small 512mb configured correctly can handle what I've thrown at it.
If you're new to managing your own server, get their $5 per month backup service (trust me, you'll need it). Because as you're learning, you're going to potentially destroy and break your site a lot and it's easier to revert to a backup than it is to decipher and fix Linux configuration issues when you have no idea where to start or even search on Google. Restoring from a backup is pretty quick as well.
My limited experience with VPS hosting (I've dabbled with Rackspace before and a Mediatemple Dedicated Virtual server as well) is pretty limited, but I have yet to see an affordable host allow you to destroy, create and rebuild instances so quickly like Linode allows you too.
Linode has consistently amazed me with their stable service and excellent customer support. I've only needed support a handful of times, but when I submitted tickets a response usually came within 10 minutes, and has never took more than 30 minutes (during normal pacific-time business hours).
I've had fewer issues with my Linode hosts than with EC2. Granted, the services offered by EC2 are much more advanced -- VPC, routing, firewalls, NAT, etc.. so perhaps this is to be expected.
I use Linode for the name servers for my DNS hosting service SlickDNS (https://www.slickdns.com) and am very happy overall with their stability and performance (much better than EC2 at the low end).
(We setup a few vps's with rackspace and have been happy so far.)