I disagree whole-heartedly with many of the comments here.
The tablet brand, model, etc. does not matter. It is the microphone that matters.
If you are buying gear for any kind of audio recording, the first thing to shop for is a microphone, and then buy the tablet/phone/PC that goes with the microphone. The microphone is the recorder, and the tablet is a microphone accessory that provides a user interface and storage. User interface and storage have nothing to do with sound quality. Your sound quality is going to come from the microphone, not the tablet.
To record speech, you can very likely get a good result with just about any USB-based microphone. There are many that are aimed at podcasters who are doing speech-based shows with mobile gear. I recommend you look for a “mobile podcast microphone” because they are going to be speech-optimized and reasonably-priced. Even with the most basic podcast microphone, you will get exponentially better recording with the internal microphone and you will get usable recordings and you won’t waste everybody’s time.
Once you have the right microphone for your needs (high-quality enough, speech-optimized enough, small enough, rugged enough, mobile enough,) then you buy it a tablet. Take the microphone tablet shopping with you and plug it in to any candidate device and test it. Basic 16-bit USB audio is an old standard, so it shouldn’t be hard to find candidate devices, but with the very broad variation in non-Apple devices, you don’t really know if you will get good results until you actually test your microphone with a specific device. And not even just a specific model like “Nexus 7” but with a specific OS and its available audio recording apps and so on. But once you find a matching tablet, you have built yourself a good mobile audio recording system. Only then can you expect to get good results.