Sorry on my bad English.
I've used 3
Adobe Flash - CS4 - the learning curve is VERY steep - and it crashes MANY times a day, often taking your work with it. It has the most flexibility and can do the most, but until you are experienced, it can take DAYS to do a few fancy transitions. I cannot make it do high resolution slide shows (1080x1900) that run smoothly. There is often "jerkiness" in complex transitions. These go away if you reduce your resolution to "web" sizes : e.g.:400x600. There is a large user community, but NO direct support from Adobe - at least none that is useful.
SlideShow Gold: a GREAT program for putting out a quick slideshow with integrated mp3 sound. Somewhat limited in transitions. The developer of this has been GREAT about answering email questions, and adding suggested features.
Halfway between the two is SlideShow Studio, from Aquasoft. This company is in Germany, but they sell an English version. Their software allows you to build VERY sophisticated transitions, including "Ken Burns" type effects of transitions, zooming in, and panning across the image, stopping and zooming in at various places. It also does MANY nice animations with text, including entry, and exit animations. It is VERY stable, and seldom crashes. The email support for this program has been GREAT. However, their Forums are all in GERMAN, so there is no user community for English speaking users. This works great for high res (1080x1900), scrolls smooth, and does even transitions. (some are a little blocky looking at high-res.) It also supports multiple aspect ratios (4:3 and 16:9). I've run it's output through a HDMI into a HD TV, and it is very good. It has a built in photo editor that allows you to add very complex modifications to an image. My only complaint is the audio editing is a little rough.
Right now I am using SlideShow studio almost exclusively, but might switch back to Slideshow Gold for speed if I had a fairly simple slideshow to produce, just for speed.
I have tried Flash before but it is very complicated, did you go on a course?