I've *just* been through the same thing myself... I'm a Microsoft Partner, so I should've jumped earlier, but JB was/is pretty good (mostly Samsungs) so it was hard to let go
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I wasn't even looking at the HTC... I *wanted* a 920, could barely justify the 820 $$$ and was deciding whether to make that leap, go with the newer 720 or go right down-market with 520/620 and get a 10xx later at the right price. The dealer showed me the HTC which was a no-brainer for my needs... The absolute cheapest 4G, 1GB RAM, great sound, great screen. I let my head decide, but a few weeks on, the heart has followed, especially WRT battery life and the awesome in-call voice quality which also translates to being able to take audio notes and dump them straight into Dragon with great results. The front facing camera is the best I've ever used (use it a lot to talk to the kids when stuck at work/away on business) and the rear one is great too.
So, whilst I still envy 920 users *a bit* I wouldn't buy one for 2 x $$$ of the HTC (i.e. my wife and I could both go the 8X for the cost of one 920) and for me the 820 seems a little pass? after experiencing the HTC. I would (now) never go down the route of accepting a 512MB/not 4G capable WP8 device over an ICS/JB Android one (esp. when the Android 3/3.5G one is 50% less).
Downsides... that Nokia app eco-system is pretty hard to beat. Whilst I can (and do) use Google maps on WP8, I'd love to have the Nokia mapping; which is probably great and easy to use. I'm sure there'll be other needs I'll have to spend time/effort satisfying (or waiting for), whereas the Nokia(s) will probably always have that stuff straight out of the box. Even more important at present until MSFT gets the WP8 app-store depth and breadth up where it should be.
I really think the 8X is the 'best kept secret" of the WP8 world and certainly the best value. If you were considering it against the 'best there is' then there may be some quite important features missing, or usage scenarios in which it just wouldn't deliver sufficient functionality for your needs, esoteric or not. But in a 'best of the rest' comparison, its a pretty compelling contender and one which, in the eyes of this 20+ year Nokia aficionado and MSFT Partner, showcases the potential of the WP8 platform as a whole to enable a variety of price/performance/value propositions that *should* auger well for consumers, vendors, partners and the industry as a whole and help keep the previously *cosy* duopoly of IOS and Android on their toes
Good luck!