Either would be better than the standard captcha. All require the user to respond to randomly generated visual data. The most important difference is that popping 5 consecutive bubbles or moles (or who cares) would be a subtle way to say “hey, sorry for the inconvenience, we don’t mean to assume that you’re a spambot, in fact we’re not gonna force you to parse gibberish characters, we sorta like you, we kinda want you to continue investing your attention here, so play this mildly entertaining game, it’s good for everyone…”

There are thousands of old school video games that provide a model for some kind of simple random generated action. Why not pick one that matches your brand? Obviously it’s got to be lightweight enough for dialup users… Pong would work.