I think at my current level I'd have to time travel all the way to around 2003 to be the very best of the time. That seems like a really long time ago, and if you watch videos from the MLG and pre-MLG days it's hard not to think "these guys have terrible tech skill, we're so much better now" but you gotta consider what made those guys champions. People like Ken, Azen, Dope, and KDJ didn't get to the top so much by being great at tech skill, but more because they were the best at knowing how to adapt, mix things up, and exploit opponents under pressure. So I think I'd have to go back to 2003, and even then I'm sure the top players would figure me out and surpass me within just a few weeks for the reasons mentioned above.
Does anyone really think Ken would get wrecked for very long in today's metagame? Sure, he might wrecked for the first few matches, but I guarantee you it would take only a mere Smashfest or two for him to adjust to today's double-shining Foxes, shine-grabbing Falcos, and bair-happy Puffs. Top players in any sort of competitive scene don't need to be ahead of their time, they only need to overcome their current greatest challenges. Ken was never threatened with an Axe-level Pikachu in his time, so he probably never had any specific tricks for that matchup, but you can bet he'd adapt really quickly if given a few hours of playing time vs Axe today. Which is why I always dismiss the argument that the old school champions wouldn't be able to keep up in today's metagame, because they definitely can with regular practice against a variety of playing styles.