I've been using HTC phones for a good few years now. They basically come in two flavours: Windows Mobile (now known as Windows Phone) and Android (backed by Google). I currently have an HTC Hero (Android) with an extended battery and prefer it over the iPhone for a few reasons: first and most important, that battery. My Hero can now spend up to 48 hours without going near a powerpoint or a USB cable. Once the battery is worn out (and rechargable batteries by design only last around 12 months) I can replace it by popping the back off the phone. Try that with an iPhone. Secondly my choice of apps isn't limited to what Apple think I should have, true you do get some iffily developed apps which cause problems but just uninstall them. I'm not sure about whether the Hero plays Flash, it plays YouTube which I though was based on Flash.
With regards to the HTC HD Mini, I personally would stay away from it for now as Windows Phone 7 is due for release towards the end of the year. You may say "ah but being cutting edge doesn't matter to me) and I accept that however it matters to a lot of people many of whom may ditch their HD Minis cheaply on
ebay.
With all smartphones, iphone or HTC (I'm not sure about the Nokias as I haven't had one since the N91) you will notice that battery life is atrocious!! Extended batteries help but don't expect the days of the old Nokia 5110 which had to be charged once a week.
Hope this helps.