Well I use VPN on a weekly basis here in Korea, lots of sites are restricted and I don’t trust the goverment too much either with my data. I mainly us it for games and encrypting my data stream for browsing and the paid version was simply more reliable and stablefor the prior mentioned. They can also be distinguished between encrypted and not encrypted versions. The later simply doesn’t work on some websites (Netflix) but is the intended useage. You want encryption on your data stream so even if people pick it up they can’t just see whats going on directly, takes some effort.
I use it a lot for IP region change, either to access other websites blocked by the goverment or simply to buy games (Steam for example). Lots of games are not registered for use in Asia, doesn’t matter if you’re playing on european servers. for this purpose, free VPNs work fine as you just buy them over the VPN. Recently this becomes more difficult as lots of the services try to prevent this (Steam … again).
I used two main GUIs till now, OpenVPN is simply easy to use but doesn’t has lots of options. You get however lots of plugins from paid services which makes connecting to them very easy. I also used SoftEther VPN (open source) which has massive amounts of free servers, for occasional use very conveneint but most of the conenctions aren’t particular stable. I used two paid services till now, the first I can’t remember. I wouldnt have recommended that anyway, dodgy servers and questionable service. The latter, IronSocket, works mostly fine. Reliable, decent ping in most games but not outstanding. It was also a bit cheaper. Bandwidth is kinda an issue, works fine for the oocasional youtube video when I forget to switch the VPN off, I barely notice it (unless its peak time in Europe). Comes with plugins for OpenVpn and is therefor very easy to use!
In short it boils down to what Jester already said.
1 - For occasional use they are perfect and you can use a open source vpn with no trouble
2 - For Ip region change it works fine too, open source is enough
3 - Playing over VPN, here I advertise paid versions, long distance they worked better, were more reliable and had less lag spikes.
4 - Watching a movie with normal to midrange bandwith usage works mostly fine, but trying to push the bandwidth to its maximums doesn’t. In most cases, if you NEED high bandwidth, don’t use a VPN.