The nexstar series have goto mounts which the astromaster doesn't. Also the Cassegrain types are more expensive I guess the glass parts are harder to make. The newtonians are essentially a long tube with two mirrors in it.
I never used the astromaster much as I couldn't get it to work prime focus with a camera on it. The focal point is too close in. Mine does need a colimation but I don't know if that will shift the point at all. I have got a digiscoping adapter for a compact, and that seems to work ok on it as it is.
Even if I got those resolved, I'll probably end up using the nexstar more often, as it is so much smaller (length) and easier to handle from that, plus it is goto so making it easier.
But, it also depends on what you want to shoot. The Cassegrain types are inherently longer focal length small relative aperture (high f number).
If I were to buy now, I'd probably go for a bigger model in the Nexstar series. Maybe once the skies get darker again.
I'm thinking of shooting galaxies and nebulae most of all, for that you need a low f-number, correct? x_X
Problem is that the Nexstar series appears to be about 3 times more expensive than an equivalent Astromaster series.
EDIT: Reading trough this forum a bit more, 5inches seem to be just too small for deep space objects unless I can properly track it and use long exposures I guess.