Hi krammmm,
I would recommend the 7 Plus. Its a good deal cheaper ($669 vs $799). All the 8+ adds is wireless charging (charging pad sold separately), a new feature in the camera that allows you to change the lighting in portrait mode, and the True Tone display, which adjusts the appearance of white based on the ambient light. At least for me, these don't seem to be worth the extra money. One thing however, the starting configuration for the 7+ is 32GB. The base model for the 8+ is 64GB. So you also get a storage upgrade with the 8+. Ultimately its what matters most to you. But personally I wouldn't buy the 8+. Its really the 7S+. Not really a huge upgrade. Calling it the iPhone 8+ was primarily a marketing strategy.
Now going from the 6S+ to the 7+ added a lot of things...So if you were choosing between those two I would definitely say go with the 7+.
Below is a link where you can compare all the different phones Apple sells currently.
iPhone - Compare Models - Apple