Both are great games
I had a nice IM for about 1 yr, I traded it for a super duper nice TZ when IM's were going for crazy money! Whiplash multi ball might be one of the best multi ball intro's ever with a shaker! I loved that!
IM is gone now, will I get another, who knows, It was fun, fast, and brutal but also pretty shallow.
At a used vault price I may pick up another in the future if the price is right, but IMHO IM was never a 6 or 7 thousand dollar game, thats super crazy money for what it is.
I now have a BSD waiting in the garage to be shopped, I am anxious to get to it, it was a lot cheaper than IM too!
Bang for buck no contest BSD
Its all about what appeals to you.