Since opinions and experiences seem to be what you are looking for, the more the merrier!
Myself, my computer is not the hot. I have tried a few photoreal sceneries for some places I know and some places I dont know. The Gand Canyon and San Francisco are places I have been to enough to recognise places and Hawaii I have never visited.
So at first I was blown away by the photoreal sceneries for all three (I have tried others that were dismal so I wont speak any more of them) but as time went on that impression faded. With the Grand Canyon the images are taken at a particular time of day so as I flew along at different times and seasons the appearance did not change to reflect that - destroyed the immersion. With San Fransisco the auto gen - well, lack of - was the immersion killer. Hawaii (by Flight Sim Jewels) I still use as it is fantastic with very good airports to go with it - but it does hit my frame rates very hard.
To compare all of the above to UTX/GEX for the USA I would have to choose the UTX product in general for a few reasons:
- easier on the frame rates
- one product covers the whole area for all the above mentioned locations
- UTX Vector gives very accurate road/rail/river detail for VFR flight as does photoreal so no detriment there.
Down sides for UTX/GEX are the costs (and they never go on sale so far as far as I have noticed), and if you know an area really well you will see the buildings are often generic and/or incorrect - for example a small apartment block instead of a barn on a farm next to town. Also if you fly with all the sliders pushed to the right you will start to see a lot of the same objects repeated a lot - like the blue water towers in the praries.
The autogen can be compensated for with fiddling but that is a faf...
In conclusion it is as others have said, a matter of choice. Try the free stuff first (and I really do recommend Flight Sim Jewels for a look) and see how you feel.
Hope this helps a little.
PS: If you are flying Bush Pilot stuff you may want to take a look for Turbulent Designs tree upgrade TerraFlora. I picked it up cheap in the sales a Xmas and it made a big difference as now I can turn the auto gen for trees all the way to maximum and bush flying is much better with trees, in my opinion!