Personally, I like the DS and DS+ pack. If you cannot afford a composer they come with 20 audio tracks each, and are worth it just for those alone. One problem you will run into is most of the DS tiles and sprites look funny next to the RTP sprites, so you will either want to go all DS/DS+ sprites or not use them at all. Might be pricy but if you can grab them while Steam has them on sale I think you will like them for the music alone, even if you don't use the rest of the pack.
High Fantasy is a style all of it's own, its best to either go all high fantasy or not at all. I think there is a game recently released that uses all High Fantasy style, so maybe try to find it and see if that is what you want to go for?
I've gotten good use out of the Rural Tile set, as it matches pretty well with the RTP in my opinion. Helps add some life to your farm and farm towns. Sure, some things are of off size, but that can be edited.
Most of the rest of the tile sets require you to copy and paste them into another tile set to use, and that might be where the bad reviews are coming from, as (at least I personally) don't feel that is well communicated to buyers, especially on steam. For example, Winter Wonderland has maybe 10 tiles in each of the sets, which is pretty bare on its own. But, if you copy and paste them into another tile set, they work better.
I think the other issue the others are having that are reviewing these tile sets is it feels like few of them match up with the RTP well, so its either convert everything all to these new tile sets, or forget about them. There's a post on here of which tile sets match up with which, which I think probably should be better communicated to buyers.
Here's the post on what matches with what.
http://forums.rpgmakerweb.com/index.php?/topic/26268-which-graphic-pack-matches-with-which/
Edit: DS+ has some sci-fi. However, in general, there is not a lot of sci-fi tiles right now.