I'm considering trying out Parallel's, but I see mixed reviews. Some reviews talk about the upgrade pricing and required freqency. Seems that this is similar to VMware's model for Fusion. Generally speaking, is that so?
A couple of us already commented on this, but to cover it again
Parallels has been supporting two major OS X versions per PD version. So for example, I upgraded to PD10 when Yosemite was released, I'm still on PD10 using El Cap. I mean, they continue to market "All new features" in PD11, but it's not needed for compatibility. The updates are $49, so that (thus far) has covered you for 2 years, so ~$25/year. I've also managed to score it with a promo for $39, and it's sometimes bundled meaning it's x % of the bundle, or you can sell some of the bundle off (reducing the price).
I've been using it since PD6, with a VM image that was transferred from an old HP, for several years, and recently used my original Win 7 Pro to a get free Win10/64 Pro upgrade/license, that's now running in a new VM, I'm also running multiple Server VMs.
Mine has been nearly flawless, and none of the issues were ever catastrophic, it mounts a drive so it's handy to access from OS X, I can D&D between machines, I use it for development (VS2010/2013, SQL, Oracle), and usually have a machine running concurrent to everything I have going on (email, safari, iTunes, term windows, messages, a bunch of background procs/services/servers).
FWIW, my server VMs were dev ISOs I simply downloaded, ran a conversion against (utility supplied by Parallels), and launched the VM directly, very handy.
My original preference for Parallels was due to the speed and the Coherence mode that allows you to run Windows windows "in" OS X (vs. in a self-contained VM window).