It's all speculation, so it's somewhat luck of the draw.

But a lot of the coins suggested here have already been pumped, so it's unlikely they will do a 100x.

No one can really predict it, so to find the gems, you really need to do some research. For that I'd recommend checking out some low cap coins that haven't been pumped, read the whitepaper, announcement, join their chat and get a sense of how the community is. If that looks good, checkout the chart and look to see if there's potential.