Comparison Between SPICE Simulators

My short answer is to just go with LTSpice, it is one of the best simulators on the market and it is free. You can't really beat that. But if you would like a breakdown feel free to read my personal opinions.

HSPICE:

• Advantages: HSPICE is widely considered one of the most accurate simulators on the market. However I have no actual experience using it.
• Disadvantages: As you said, it is expensive, proprietary, and as far as I know has no schematic capture features.
• Overall: If you REQUIRE reliable results (Military or high end industrial) then HSPICE is the way to go. Otherwise, I would avoid it.

LTSpice:

• Advantages: If you are doing power electronics this simulator is tuned for simulating switching events, as well as some other things which make it perfect for this field. Additionally, it has (IMO) an intuitive interface and doesn't try to hide the netlist from you. Plus, it is FREE.
• Disadvantages: ? I haven't been made aware of any, it isn't considered quite as accurate as HSPICE, but it isn't inaccurate by any means.
• Overall: This is the simulator I would suggest. It is easy to use, it is free, and it is supported by a much larger company. (Linear Technology)

ngspice:

• Overall: I don't know enough about ngspice to give a full overview. I only recently downloaded it and am still working on compiling it for my system. Obviously you have found one of the drawbacks is being limited to the command line.

PSPICE:

• Advantages: Well this is as close as you can get to the original SPICE. PSPICE is powerful, has a well established simulator, built in results viewer, and an extensive model library.
• Disadvantages: Unfortunately it has become so bloated in recent years that it is difficult to recommend. And as you would probably like to have it on your computer, I would bet this one is out of your price range unless you have $20,000 laying around.
• Overall: Powerful and well established, but going downhill fast. Expensive.

I would say that depends heavily on what you need it for. Often the expensive spices are part of some e.g PCB design tool. I'm just trying out MultiSIm from NI (expensive orcad type tool), and it has lots of pretty virtual instruments (e.g scope, distortion analyser, etc) and monte carlo analysis (which LTspice does not have a "convenient" version of - it does have some functions you can use though as Vlad points out, here is a link on using them) but to be honest I find that 99% of things I could do on LTspice.
I find the LTspice setup is by far the quickest out of any spice I have tried, once you get used to the key commands. R for resistor, D for diode, is much easier than clicking the picture (or even selecting from a pop up box in MultiSims case, arghh) and dragging to the right place every time.
You can have a circuit done in seconds this way.

The manual is not as pretty either, but all the info you need is there regarding how to use, eg. the .param, .step and .measure commands for doing things like running an analysis many times and varying parameters. I just tried to run a transfer function analysis in MultiSim in this manner (i.e. run may times and vary a parameter then plot results) but despite reading/wrestling for hours with it, I couldn't manage it, but a quick addition of .step V2 -15 15 1 to the sheet made it possible in LTspice.
I'm sure some of the above is simply as I'm new to MultiSim, and no doubt I am missing something (as the above example simply must be possible in a tool like that) and no I don't work for LT :-) but it has been the only spice that I have used regularly for the last few years. The main point is that it will do all the normal stuff as good (and probably faster) than the expensive tools, but if you need the extras (e.g. monte carle, PCB level anaysis based on actual routing/IBIS models - Altium does this excellently) and all wrapped up in one design tool then you may need more than if can offer.
In my view it can't hurt much to have around even if you do need a more powerful tool anyway.

I don't have experience with HSPICE, but use LTspice and NGSPICE very frequently. In my field (power electronics), I have observed fellow engineers actively refuse to work with the company-supplied Pspice after being exposed to LTspice.

Unfortunately, LTspice is closed source, has no scripting possibility, and you can't add (your own) code models to it. When you need these more advanced options (not many people do or care) NGSPICE is the way to go. It's open source, incorporates XSPICE, KLU, open-mp and CUA, and has a C-shell type interpreter with very advanced possibilities (but IMHO a horrible user interface). It does not have schematic entry but there are solutions for that (e.g. LTspice). NGSPICE can be used with gnuplot for very nice, programmable, graphical output.