I would not recommend Wyches via portal as you're still going to want to rely on a vehicle(s) to soak up overwatch so you might as well save the command point and take them in raiders. But if you know you're going to have plenty of little vehicles where you're going to want your Wyches to be anyway, then it's fine, and I'd recommend taking the 20 as Cursed Blade. However, the other thing to consider is the 9" charge distance - even with re-rolls or a re-roll it's a little risky. I prefer the surety of raiders and venoms.
My 8th edition fandex is complete enough for appraisal (note that I completed it before any previews had been released) . I'm sure there are inconsistencies, please let me know where they lie as you find them. Thank you! Click here for fandex