I am looking at new lines for a spinning rod. I fish in a rocky river but also fish some lakes too. Should I use braid to long leader or straight fluorocarbon. Also, what is your favorite leader or straight line. Thanks!

Braid to leader is my vote. You’ll use less line that way. Breaking off straight line means less and less on your reel every time. It also allows you to be flexible in changing your leader length and strength according to what you’re doing and where.
 

Imo, FC is not always necessary so most of the time I’m using a mono leader. My favorite leader to use as of late is Berkley XL. Just reliable and works for me. I also use Yo-Zuri Hybrid. When going with a FC leader I like Yo-Zuri Topknot. Not a premium line and it is a bit wiry but that’s not a problem with leaders. It holds up well enough to abrasion for me and has not failed me. I think with any leader line you choose as long as you know your knots and take care of your line, it’ll be fine. 

This ^^^ but main reason is not just to save line but less problematic with line twisted, windknot. You can go as high as 15-20lb braid with 10-15lb leader while straight mono/fc you limited to only light line. I also prefer mono/Copolymer as leader, comparable abrasion resistance but a lot stronger knot than FC. With that short of leader I don’t think FC have any advantage whatsoever over mono/Copolymer. 

best fluorocarbon leader I've used is YGK. 

 

 

V12 especially for abraision resistance. 

 

Seaguar Blue and Gold are close to these, and I would recommend Seaguar Gold for improved abrasion resistance. 

 

adding a ps - the most limp and most abraision-resistant fluorocarbon main line I've tried is Toray ExThread. 

Seaguar Gold Label 

For leader there is no other better than Pline shinsei! I have put this line through the ringer for the past 2 years with absolutely zero failures!

I've used it on the rock walls in Miami for big peacocks, snook, giant carp and tarpon. I use it as a leader to my braid throwing up to 6 oz swim baits and have backlashed plenty of times with no break offs. 

For my main line I stick to Abrazx fluoro or Trilene gold depending on technique. 

In my attempt to be cost effective, I use Daiwa J-Flouro as my leader line.  it is a schooch thinner than the above mentioned Sensei Leader.  (10lb leader is what I use).  I simply love it that it comes in a 100 yard spool for less than $20.  I have hauled in big LMB with it including my 7lb PB that got tangled had in Delta Foliage.  I'll stay with it since I tend to run long leader in front of my braid.  

For leader material I go cheap.  The kast king or pline flouro clear is all you need.  They are both flouro coated co-polymers. I’ve used both in lakes with 20 ft visibility.  I believe they both cost about $10 for 220 yard spool 

Sunline FC Leader. 50yd spools. I use it on all of my spinning combos. 8lb or 10lb tied to 15lb braid with the alberto knot.  

I use the Kastking line of braid and their Kovert FC. Haven't had any issues. I usually can get on sale.

 

@Finessegenics and @ErieCan are giving you my answers.  Braid to leader is what feels best to me also.  I have to say that I use Yo-Zuri Hybrid as mainline on almost all of my baitcasters but I have had terrible luck using it as a leader.  That is clearly because it does not like my Alberto knot.  I have used many different flouros as a leader and the ones designated as "Leader" are much more reliable.  I have no idea what's different, but it is.  The Sunline FC is my favorite.  Never a problem.  

For braid I like Sunline X-plasma 16lb and 10lb Seaguar Gold Label for leader. 

30lb Power Pro high vis color, 10-12 lb Trilene Big Game mono leader with FG knot.  Done.