I love the NunnFiner softgrip ones. They are not lined with anything and are thus quite thin and extremely pliable. They are wonderful, very popular with eventers. I like them so much I change them from bridle to bridle.
Wear gloves in the rain, though, they can get a little slick with bare hands.
I like the pair of NunnFiner softgrip reins a barnmate uses. I borrowed her bridle once and quite liked them a lot. I hate riding in gloves and these are easy on the hands and have grip even without gloves. They are thinner than normal rubber reins and not stiff at all.
Try searching the eventing forum for this topic. You'll find tons of feedback there on all the reins mentioned here. For reference, the rubber-over-nylon type that you're describing are called Eventa reins or Equus grip reins.
nunnfiner reins are nice. Also, I was at VTO saddlery at an event once and they carried pessoa reins. they are so nice! very flexible. I have little bitty baby hands and I am super picky about anything being stiff. I was impressed! I would try them out.
KL Select has a pair of very soft, very flexible rubber reins. They arent as thick as most brands. I've got a pair and really like them. They are well constructed and come in different widths based on your preference. I was all set on getting a pair of Nunn Finer's till I ran across these on sale. The suppleness that these have made the decision easy.
If your willing to look around, hands down the softest rubber reins I've ever had were a pair of Dominus. I got a Dominus Figure 8 on Ebay for kicks, and when the reins came out of the box I was AMAZED! Still my favorite 7 years later.
I have a pair of "rubber" reins that I absolutely love for their softness - they almost feel like neoprene? They are not pebbled like regular rubber reins; they are smooth and very grippy when wet.
I *think* they are made by T de T, but I'm not 100% certain about that. If you like, I can check when I go out to the barn. I bought them years ago at a tack shop in Atlanta and they have held up really well despite constant use. I highly recommend them.
********** We move pretty fast for some rabid garden snails.
Thin Line. no pebbles. soft and smooth. Even someone as experienced as Dorothy Crowell and believe me she has rode enough xc to know her reins - she recently rode our horse at a clinic and she raved about the reins and wanted to know what they were.
We got them at Rolex for 1/2 the money. Some things make that trip pay for itself. then the fun is all free!
About the only time losing is more fun than winning is when you're fighting temptation.
-- Tom Wilson, actor & comedian