Clears have little ridges on the stems which can hold certain keycap types very tightly. DSA profile was originally designed for "industrial" use, so they're designed to fit tightly on the stems. When used in combination you can end up with keycaps that are very tight on the stems. It's not an issue if you have a loose MX Clear switch and use it to loosen up the caps a little before installing them by cycling them on and off the switch a few times each.
There are a whole lot of keycap options out there. I recommend you wait for your board to arrive and take your time browsing this subforum, the Group Buys subforum and elsewhere before you commit to buying a set of caps.
Some basics:
There are three main properties of keycaps that are important: Profile, material and print type.
Profile:
OEM: Most board come stock with OEM profile keycaps. OEM is not standardised, but most of them are very similar to each other. They are tallish and mildly "contoured" (each row has a different height and keytop angle) with "cylindrical" dents on the top of the caps.
Cherry: Originally made only by Cherry Corp, but now also made by BSP and GMK. Leopold's new PBT caps are also almost identical to Cherry profile. It's a lower profile than OEM, but also contoured and with cylindrical dents.
DCS: Made by Signature Plastics and often used for Group Buy sets. Very similar to Cherry profile, but with a steeper angle on the bottom two rows.
DSA: Made by Signature Plastics. Uncontoured (all rows have the same angle and height), low keycaps with spherical dents in the keytops. There are some other manufacturers with very similar profile caps (Cherry Corp made a similar one for their M8 switches, for instance)
SA: Made by Signature Plastics. Tall, contoured profile with spherical keytop dents. It is often used as an uncontoured profile, though, like DSA by using all row 3 profile. The contouring differs from DCS, Cherry and OEM in that the base angle is "flat" instead of angled away from the user, so the keycap tops make a smooth curve instead of being "stepped". Many old terminal boards used a similar profile and you'll find it on some old typewriters, too. It seems to have been designed for use with stepped boards or boards with angled keycap mounts which explains the "flat" base angle, but it actually turns out to feel really nice to type on despite the difference in angle with modern boards due to them being laid flatter than the old terminals and typewriters.
Material:
ABS: Stock material used for all profiles of keycaps. It is relatively fast-wearing and the least dense of all keycap materials. Floats in water. It's more malleable than PBT, but less than POM.
PBT: Denser, more hard-wearing material than ABS with different surface "feeling", tends to feel more "dry" and less "greasy" than ABS.
POM: Densest of the 3, quite hard-wearing and durable. Feels more "smooth" and teflon-like than the others, without "gripping" like smooth ABS can.
Printing:
Pad printed: Most standard rubber dome keyboards and laptops have pad printed keycaps. The legends are printed on the top with some form of ink or paint and then covered with a protective coat. The legends are therefore raised above the keycap surface and they can wear away fairly quickly.
Dye-sublimated (dyesubbed): Often used on PBT keycaps. An ink which is darker than the keycap material is heated and applied to the surface of the keycaps to allow the keycap material to absorb the dye. This results in a long-lasting legend which penetrates the actual material of the keycap and thus is not raised and is very long-lasting.
Lasered: There are three main types of lasered legends. The first uses a laser to etch the surface of the cap which is then infilled with ink / paint. This provides an almost-flush surface and is harder wearing than pad printing, but not as good as dyesub and the legends can usually be felt. The second "foams" or "burns" the keycap material, producing a darker colour. These can be slightly raised and penetrate a little into the surface. The third is when the keycaps are first coated in a layer of paint / dye that is UV cured and then a laser is used to "ablate" the legends into the surface by burning away the unwanted part. Backlit ABS keycaps are often made this way. This results in an inset legend that wears away relatively quickly (depending on the toughness of the paint used).
Double shot: The king of legends. Double shot keycaps are made in a two stage process where the legend and some support material are molded from one colour of plastic and then the main part of the keycap is molded around them in a different colour of plastic. ABS is the most tolerant of this process and is thus the most widely used for making doubleshots. The legends are flush with the surface and last until the keycap is worn down to almost unusable levels. The most durable of all types of "printing".
For the most part, keycap profile, material and legend type are a personal preference. Many people try a whole lot of them before settling on just a few as their favourites. That said, the most important factors when choosing keycaps, IMHO, are the quality of manufacture and thickness of material. The thicker the better. In this regard, GMK doubleshots and SA profile doubleshots are the best ABS keycaps available. In PBT, thick, Cherry profile dyesubs are what to look for. Those Leopold caps are very good, too. Unfortunately, there aren't a lot of POM sets around (my favourite material) and those that are, are usually laser-infilled.
My personal favourite is contoured SA profile ABS doubleshots. I just wish they made them with POM.
