There's no way older folks can choose anything but SINISTAR. I loved that game in the arcade. I've never seen the friggin' huge cabinet that PicnicCyborg posted, though. Crazy.
Now, I like Sinistron, but it definitely suffers from the ANONYMOUS, NAMELESS protagonist & enemy hordes syndrome.
That said, I've grown fonder and fonder of Sinistron over the years. What I thought was a mediocre/average shoot-em-up on TG-16 back in 1991 has held up a lot better than I thought it would in 2014. I am unabashedly fond of standard 80's shoot em up conventions (I feel the same about CyberCore).
SINISTAR will always have a special place in my heart, but it is such a very different experience that I can't even find a common thread, other than the fact that I get FRUSTRATED by both games. Ha!