I moved from SH over a year ago and my answers are
1) Control panel: Linode's is better, the layout is easier to use, it has more features, and it has a support ticket area where as slicehost it's mainly email support.
2) Support speed, well I've raised about a dozen support tickets in my time, all responded to in minutes and solving my issue off the bat. So yes awesome
3) Reliability, compare the status pages status.linode.com vs status.slicehost.com Slicehost has quite a few problems with their slice manager and api, linode doesn't.
4) Communities, last time I paid a visit to the SH community it was dead, here it's getting busier and busier both on IRC and here (I mainly hang here).
Other good points:
a) London data centre
b) More ram etc for your buck
c) Lish (you'll never have to use the crappy ajax console again)
d) I think linode gives you an extra backup slot
e) Not owned by rackspace
f) Not owned by rackspace
Shameful plug of referral link
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