Best value period is the Nexus 7 2013. It is only a 7 inch tablet, but it is a great 7 inch tablet and that size does have some perks (great for reading books, using one handed).
For 8-ish inch tablets. I'd go with the Galaxy Tab Pro 8.4. It's only $250 now at Best Buy, has the better Snapdragon 800 (IMO) processor (vs most of the other Galaxy Tab models with Exynos). And is pretty compact.
9-10 inch. Hmm, this is hard. Nexus 9 just isn't as good as I hoped. Neither am I excited about the Galaxy Tab Pro 10.1 or S 10.5. And most other 10 inch tablets are a bit long in the tooth or just cheap POS.... I guess it's a toss up between the Nexus 9 and Tab S 10.5 (its slower but has the AMOLED display and expandable storage).