Logitech G11 vs. Logitech G15: Which series is better?

I know you’re all probably sick of answering the same old questions, but I’m genuinely stuck here and could use your take.

So, I just swung by Best Buy earlier today. The guy working there was telling me that the main difference with the G19 is that it’s more compact—you get that little LCD screen for your CPU stats, which doesn't really matter to me unless I'm obsessively tracking temperatures, while the Logitech G15 is just a solid, reliable choice. He even tried to upsell me on the G13, but honestly, you’d actually have to learn how to use that weird little nub as a mouse or something.
But hey, don't take my word for it—I might be totally off base here. I've got a perfectly standard keyboard and a Microsoft mouse that costs about $17 these days, and I'm still absolutely crushing it when it comes to coding. I'm just passing along what the guy told me!