In general, the darker the color of the metal of the muffin tin the more it will brown its contents. You also want to look for a thick, durable metal as this will aid in even cooking. Finally, look for a tin with large, wide handles; the last thing you want to be doing is sticking your thumbs into a muffin when trying to insert/remove the tin from the oven! Most muffin tins these days are non-stick, so it may be hard to find one that is not. With that said, non-stick technology has advanced a bit since the Teflon-only days. For example, many modern non-stick pans/tins instead use other metals and ceramics that are not known to be harmful. Furthermore, some modern muffin tins are marketed as "metal-safe", meaning that one can use a metal utensil on them (e.g., to extract the muffins from the tin) without damaging the non-stick coating. Finally, muffin tins will likely never be heated to the temperatures at which the "dangerous" non-stick coatings release harmful gasses.
In my experience, rice quality has a pretty substantial amount of variation, but the cooking device has little to do with it.
While I'm sure that most rice cookers on the market from Japanese firms are optimized and tested for short-grain, japonica rice, I've never had issues cooking basmati or jasmine rice in one, and I've even used them for farro and mixed grains.
I doubt that the rice cooker has much to do with it. I've made rice in heavy cast-iron enamelware on the stove, in a cheap Southeast Asian electric steamer without any fancy "fuzzy logic" electronics, in a fuzzy logic rice cooker, and an mid-range IH rice cooker, which is what we use at home now, and the quality of the rice and its age has a greater impact than the cooking method. I would say that the IH rice cooker produces superior results over our old fuzzy logic cooker, but it's certainly not an order-of-magnitude kind of difference.
Assuming you're located in the US, my benchmark go-to rice brand is "Tamaki Gold", which is from a japonica strain called koshihikari, and I think most of this brand's rice is grown near Sacramento, CA. It's more expensive than the typical Botan or Niko Niko brand calrose rice that's ubiquitious in Japanese supermarkets, but I find the quality far superior, and it's still a good value. My wife tends not to appreciate the Niko Niko or Botan calrose rice very much at all, so we don't eat it at home, but probably 80% of Japanese restaurants in the US are using it or a similar product.
Generally, I'd recommend staying away from the absolute cheapest brands, and choose something that's a couple of notches above. We've used imported rice from Akita or wherever and gotten very nice results, but the differences were far subtler than the price (on the order of $10 vs. $35 for a similar quantity). The sweet spot for quality is near the median price, assuming you're in a shop that offers a wide variety of options.
Edit: Sorry, until your edit, I didn't realize you were working from parboiled or converted rice, I assumed raw rice, as I've never heard of anyone cooking the quick cooking rice products in a rice cooker. (Rice cookers often have their own "quick mode" which shortens cooking time with normal raw rice at the cost of a slightly reduced textural quality). Considering that's what you were starting from, consider using other supermarket brands of rice that meet your target grain size and stickiness/fluffiness, but aren't marketed for speed or convenience.
Best Answer
Volume
Volume is usually the primarily advertised statistic for rice cookers. This indicates the volume of cooked rice that can be prepared in one cycle. Common sizes include 5.5 cups and 10 cups. 5.5 cups is completely adequate for a family of five people for a single meal.
Bowl quality
Bowls in entry-level models are typically aluminum. Higher end models will be stainless steel. The same heating properties present in pans are relevant here. Aluminum heats quickly, and unevenly. Steel provides a more even heat.
Also of concern is the interior of the bowl. Nearly all bowls have a non-stick coating of varying quality. I've seen the coating start to flake off within a handful of uses on the cheaper rice makers. Higher end bowls can have a durable coating that lasts years or longer.
Cooking logic
The simplest and cheapest rice makers will have basic static logic. You put rice in, push a button, and the logic simply applies X amount of heat for Y minutes.
Higher end models also have additional functions including:
Cooking/Heating method
Most rice makers use a simple coiled electric heating element located under the bowl. This is a major cause of overcooked/browned/burnt parts where the rice contacts the heated area. This is exacerbated by cheaper aluminum bowls.
Higher end rice makers use induction heating. Induction is a rapidly alternating magnetic field which uses the entire bowl as the heating element. This heats much more evenly and is far less likely (almost impossible) to burn the rice.
The highest end rice makers add pressure cooking capabilities. Pressure cooked rice purportedly is softer, and retains softness longer than regular cooked rice.
Brand & price
This is probably the most important. In my experience, you actually get what you pay for. Without fail every American brand rice maker (presumably made in China) I've used has been atrocious. The most positive thing I can say about one is "it worked great for the first batch".
There is one Japanese manufacturer that stands out from the pack: Zojirushi. I cannot overstate how amazing their product is. It literally just works, every time. I received the Zojirushi NP-HBC10 5-1/2-Cup Rice Cooker and Warmer with Induction Heating System as a gift over two years ago. I have used the hell out of this thing and have never had a less than perfect batch of rice.