@Steensj2004 , everyone has a different opinion and all of them are valid, but I'll just throw mine in.
I don't like using mesh for flavor testing mixes. I think the flavor is OK, but the temp ramp up time is too long with mesh unless you run fairly high wattage. And the deal with wattage for me is I want to flavor test at around 30~35W, which is kind of the center of MTL low watt and DTL guys. Since flavors change with power, this is kind of vaping at a mean average for flavor and there won't be too significant flavor change going higher or lower wattage. There will be some though.
For an RDA. Just about any single coil with a reduced chamber will do. My preference right now is the Drop Solo which is a single coil, small chamber RDA. But there are lots of good choices. I build it with 28Ga SS316L at 7 wraps, which is around 0.7Ohms depending on leg length, and very quick ramp up at 30W and flavor is very good. But there are lots of good single coil RDAs available, and whichever one you pick you will need to build a few times to learn it's quirks. So just go with what you read in the RDA section of the forum and is relatively cheap. So it's not so much the RDA you choose, but how you build it really.
Of course use good cotton, COTN, Cotton Bacon, Muji, Koh Gen Do, or whatever good cotton you find since cotton will change the flavor.
And finally, take your time researching an RDA since once you choose one for juice testing you will ideally stay with that for a long time. Using the same atty, with the same build and cotton is the only way you are going to be able to taste the subtle difference as you dial in a mix.