How is your sibling these days?

Carver - templar
Bethany - circle mage

There are legends... (I have a Hawke, who was on minimal friendship with him. He wanted to save him, so supported Templars at finish.)

I also have dead Carver... my first playthrough. Carver wanted to came, and Anders said, he hates the Deep Roads, so: I took anyone else. 

(And I prefer Bethany as Circle Mage, but it was difficult to leave her home. Kirkwall seems more dangerous to a mage, than the Deep Roads, and I hate to use metaknowledge, many people said, that this is better, she will more confident – and less grumpy...)

Bethany is a circle mage. I haven't played a game with a living Carver yet.

Carver, Warden, 100% Friendship (I get all the companions locked in with friendship in the same game but it's hard to do...Hawke has to be sneaky with who is picked for certain quests)

I did initially have Bethany as a Circle mage but it wasn't all that interesting. Making her a Warden might her slightly more involved in the story and deepened the connection between Stroud and Hawke. Plus, I kinda like Sad Bethany.

Carver - GW

Bethany - DEAADDD

Since I almost always play mages, it's Carver for me. He usually ends up as a Grey Warden, though I've had him as a Templar once or twice just for kicks.

I played all outcomes for both siblings (except died in the Deep Roads) and my favorite is Carver as a Grey Warden (canon playthrough) and Bethany as a Circle Mage.

Bethany - Circle Mage

Carver - Grey Warden

I still like to think that Carver ultimately becomes a Warden even if he does join the Templars however. The events at the Gallows and the subsequent Chantry schism when the Templars decide to go rogue would be plenty of reason to leave the order. If brought along for Legacy, Templar!Carver can admit to having always wondered about becoming a Warden instead.

The opposite would serve as a lore-friendly reason and counterpoint for why Warden!Carver has access to Templar abilities (aside from gameplay convenience). As a Warden, he wanted to learn how the Templars handled magical threats and brought them onto an even-footing, which would help him deal with Darkspawn Emissaries.

Rival Templar Carver? He's a little jerk bastard, perfectly match to my Hawke(s).  
If Hawke reveals all parts of Malcolm's will, Carver shows his love toward her brother/sister for a moment... And as Templar he admit, that not really this was, what he expected, then joined to the Order. So, yes, as Grey Warden he finally find his place in the world, as Templar, he a bit disappointed.