I need your advice in terms of buying a right VPS from a decent hosting provider and two hosts are in my mind: libertyvps.net and tietokettu.net, so what should I do? 

I'd recomend you to use a VPS from a decent hosting provider with the first month discount - hostingsource.com.
Top notch support, affordable pricing, and I haven't seen a bit of downtime.
 

Why not give GTHost.com Atlanta VPS a try?
Affordable pricing with top-notch performance — I couldn't ask for more!
The uptime has been impeccable, ensuring my business remains operational 24/7.

hostpro.com runs their VPS infrastructure on NVMe SSDs, which is great for speed and I/O performance. The fact they store daily backups for 30 days adds a serious layer of safety. Locations in the US and EU make it easy to host close to your audience.