what are the pros & cons of mono vs flurocarbon line ?

Fluorocarbon:

Less Visible

Sinks

More Sensitive

Impervious to UV and the elements

Does not absorb water

Mono:

Generally more manageable

Generally stronger per diameter

Generally more abrasion resistant

Generally has better knot strength

Floats (topwaters)

Don't forget the biggest advantage mono has over flouro: cost.

I can buy 1000+ yards of Berkley Big Game for less than the cost of 100+ yards of Trilene flouro.

Flourocarbon is great, but I can't justify the cost on more than one rod.

Fluorocarbon:

Less Visible

Sinks

More Sensitive

Impervious to UV and the elements

Does not absorb water

Mono:

Generally more manageable

Generally stronger per diameter

Generally more abrasion resistant

Generally has better knot strength

Floats (topwaters)

C'est Fini (It Is Finished)  

Fluorocarbon:

Less Visible

Sinks

More Sensitive

Impervious to UV and the elements

Does not absorb water

Mono:

Generally more manageable

Generally stronger per diameter

Generally more abrasion resistant

Generally has better knot strength

Floats (topwaters)

So this is why I see alot of people using mono with a fluoro leader?

Fluorocarbon:

Less Visible

Sinks

More Sensitive

Impervious to UV and the elements

Does not absorb water

Mono:

Generally more manageable

Generally stronger per diameter

Generally more abrasion resistant

Generally has better knot strength

Floats (topwaters)

So this is why I see alot of people using mono with a fluoro leader?

Or braid with a fluoro leader. It is more economical and puts fc where it is more important, at the end.  Put on an extra long leader and you won't have to retie as often.