I don't know much about Symbian devices, so I will defer any talk of the Sony P990 to someone else.
The XDA Exec is the HTC Universal and the SPV 1000 is the HTC Himalaya. If you do searches on them under those names, you may get more results.
Now, the Himalaya is a bit older. They do have an upgrade for it to WM2005 I believe though, so it wouldn't be too bad, but older.
The HTC Universal is where it's at. It's the newest, latest and greatest. I don't know the prices you're looking at, but I'd venture to say that the Universal is probably twice as much as the Himalaya. If you can afford it, go for it.
You may also want to look to see if your carrier has the HTC Blue Angel. It looks kind of like the Himalaya, but slides up to reveal a QWERTY keyboard. One thing I don't like about the Universal and Wizard is that the keyboards are in landscape mode, making it quite difficult to use one handed. I like the BA (I have the Harrier which is the CDMA version of the BA without WiFi) because it is quite easy to be used one handed. For some reason, the BA got an upgrade to WM5 and the Harrier did not. If you tell me what carrier you are looking at I can tell you if they have a BA you may be able to get a hold of.
Like I said, if you research the devices under the HTC names, you will probably get more results.
Also, check out
www.pdaphonehome.com, and they have both a Windows Mobile section and Symbian section. You can read about various peoples experience with the phones and what they like/don't like what the problems are, etc.
This is the HTC Himalaya forum:
http://pdaphonehome.com/forums/forumdisplay.php?s=&forumid=126
This is the Blue Angel forum:
http://pdaphonehome.com/forums/forumdisplay.php?s=&forumid=167
They do not have a Universal or P990 section, since there's not a lot of carriers that have them yet, although you may find some information floating here and there.
XDA Developers is also the single biggest resource for HTC-made devices. Check out their forum listings here:
http://forum.xda-developers.com/index.php
Hope that helps you make your choice.