Highly reliable and scalabe VPS?

[Tilsun]

We are moving ahead from beta launch of a business app and will start getting more traffic. Initially app will provide xml to 1k-2k daily mobile users with 10% using web access and this figure may go up 10-20 times by end of this year. Our users are paid users. So we can afford to pay for hosting. We use php/mysql. What kind of solution can you suggest for us? VPS like linode/softlayer or dedicated server?
Reliability, uptime, security and peace of mind are our top priorities. But we need highly scalable solution as requirement is going to change fast.
Thinking to try Profvds.com VPS solutions, but still wanna know your views on them? Are they trustworthy?
Any other recommendations please?

Thanks and regards