When thinking about slavery in the 18th and early 19th century (and related topics, like the rise of abolitionism, etc), you really have to keep in mind that we're at least talking about two related but district atrocities -- not only the practice of plantation slavery itself in the New World, but the Atlantic Slave Trade. The latter in itself killed, even in the most conservative estimates, as significant fraction of those transported en route to the New World, as well as making the most brutal conditions of plantation slavery economicallg feasible by providing a steady supply of "replacement" labor; not for nothing has this period been likened to a "black holocaust".
An abolitionist movement that took longer to really get underway, combined with the lack of a ripe geopolitical context provided by the Haitian Revolution and Napoleonic Wars, would most certainly mean the height of the Atlantic Slave Trade continues longer (possibly 25 years). Whether the British could have more quickly (ie less than another 25 years) abolished slavery within their empire following this, or whether they even could have abolished slavery in the North American colonies as easily as they did with the colonies they had OTL -- well, I'm not going to say it's impossible, but I find it less likely than the alternative.
There are other negative aspects of TTL -- the lack of a much later industrial revolution in North America (regarding global economic progress more generally) -- as well as at least some positive notes -- such as the native nations doing far better -- but it's hard, to my mind, to beat, in terms of pure human misery, the effects of the Triangular Trade circa the 18th Century. And while all this is only speaking of how the late 18th and 19th century is affected, anything beyond that (eg the Nazis) simply get too far from our PoD.
So I'd have to go with "worse".