The grass and wood textures in your screen shots are the best of all the ones you've made. In MineCraft, it is very rare to see grass textures without grids. Not sure if it is an aspect of the way it is rendered, but you can see clear lines between the blocks, especially in Super Flat, even with the default texture (which is essentially noise). You can remove that horizontal line of prominent clumps of grass you have in your texture, but if you don't completely obliterate the grid, don't sweat it.
Your wood texture, although probably the best of all the ones you have showed so far, needs a lot of work. Use google images to look at real wood planks (not those fancy faux textures that are a buck a piece). Here is one I found:
http://versporttvonline.com/wooden-plank-background/Now, I know these are planks constructed for houses, not driftwood, but you get the general idea. There are clear lines that go the length of the wood. You have tried to recreate it, but it looks like Thor just went round and started bashing your walls. Not only do they have WAY too many colors, but you just threw random shadows and highlights. Wood doesn't shine, unless it is polished. Your texture pack doesn't seem to have that vibe. There are some lights and some darks, but these lights and darks are not lines, they are areas. Make maybe a few wood knots or darkened spots, and a few lighter spots. Use the darkest and light shade(s) VERY sparingly, and do not have any colors that looks like shadows or highlights, unless a board is really sticking out a lot.
Stone is not cobble stone, there are not chunks. Stone does have irregularities, but not enough to make it look like tons of small stones, it is a wall of stone. Here is another reference image:
http://fc00.deviantart.net/fs7/i/2005/160/a/f/Stone_texture_by_enframed.jpg(not inserting image because it is huge)
You can see there are a few places that jut out, and the surface is rough. Resist the temptation to go crazy with noise, if you like dithering, go with dithering. Have shadows, but light shadows. Tiling is a pain in the ass, removing the grid, all that jazz. It is hard, it takes hard work, time, and dedication. Make the texture share aspects between tiles. Don't just texture a tile as a standalone, and then try to make it fit. Maybe have a piece that juts out continue on to the next tile. Make sure the elements are even, not concentrated in any one place. Don't make a large thing that draws someone's attention directly to it, make the whole tile equally interesting.
Coal is especially difficult to do. Coal doesn't appear in nature anything like how it is represented in minecraft. There are usually giant deposits of solid coal. It isn't a ore at all, it doesn't mix with the stone like iron and gold do. Some texture packs try to represent these large deposits with just one chunk of coal, but, surrounded by stone, this has the most apparent grid without outlining each block in black. I don't see anything wrong with how you are doing it now, just be sure to fix the stone texture (I know this is not your current stone texture, but, as I stated above, stone is not separated into little chunks.)
Iron is not found in nuggets, and you have done a good job at distinguishing your texture from these "nugget" textures, but this isn't very realistic either, and the grid is horribly obvious. Having these "veins" is good, but try to blend them in with the rock more. The iron is at the same level at the rock, in your texture it looks as if it were a bit receded. Don't make all the veins terminate so close to the edge, maybe make them loop back or fade before they get so close to the edge.
Your cobblestone is excellent, nice variation in length, I like how some seem to be pushed out a bit. Maybe do the opposite on some, making them look pushed back (add a shadow to them). The moss seems a bit to green to me, as it occurs in dungeons, not exactly full of lively bright green moss that has tons of sunlight. Tone down the brightness just a tad. I can't tell with this little amount of bricks, but it seems that there might be a grid problem with this moss. Again, use the premise of spreading details among multiple tiles, not just one.
Just like the stone on the coal and iron ores, the dirt suffers from gridding, and smoothness. It looks to me as if it was a simply hue change and copy paste. Dirt is rough, it has clumps, tiny pebbles, etc. Again, don't draw attention to one particular space, spread the details out across the tile. The roots in the side grass tile are ok, but seem beveled (highlight all on one side shadow all on the other), and plastic. The grass also suffers from this plastic look. Just putting lines of highlights and shadows doesn't convey "grass", it conveys "green substance". Try doing something like your top grass. Also, the colors don't match, this side grass is bright and green, the top grass is slightly saturated.
Sorry for being so nitty-gritty, and some of my answers don't help much in how to fix it. Trial and error is key, try different ideas. If you don't think it looks right, don't settle. Keep working at it till is does. And that wall of text wasn't meant, it just kept pouring out.
Credit for Images
Wood Plank:
http://versporttvonline.com/Stone Texture:
http://enframed.deviantart.com/