The difference between the HD and XLT models is the optics. The HD models have aplanatic optics which corrects for coma and reduces the spot size of stars over the FoV of the scope. So, when you look through the HD models
visually, or when taking pics, the stars look pinpoint across the FoV and are not distorted in any way. The XLT model has ordinary SCT optics and is therefore not as well corrected for coma and such out to the edges of the FoV of the scope.
The Edge HD model is perfectly good for visual observations and is actually better than the XLT. The image tends to be a bit brighter and sharper because the optics are corrected for those errors that the normal optic are not. They're also excellent for astropics. The XLT model is also great for both visual and astropics, but not quite as good as the HD model. The main difference, apart from the optics, is the price. The HD model will be a little bit more expensive.
Both models need an equatorial wedge if you want to take long exposure pics. Unless you buy a derotator for use in alt-az mode. Neither need anything other than their alt-az mounts if you're just using them for visual obs.
If all you want your scope for is visual obs, either will do. It just depends on your budget. If you want it for both visual and pics, then the HD will be a better buy in the long run, but get it with an EQ mount. The really cool thing with both scopes is they're farstar compatible, so you can remove the secondary mirror and replace it with a hyperstar lens. Then you can take wide field piccies at around f2 with your scope...have a look here...
http://starizona.com/acb/hyperstar/index.aspx