The tools are as accurate as one defines the regular expressions to identify code and parse it correctly. They are working usually flawless, which means they are always right. If something isn't working and I start to get grey hairs about a problem to solve, I can be sure, that sed, awk or grep is always right in the end
Easier... hm, maybe awk is looking a bit more structured and has commands like other languages have. sed is like ed with only 1 letter for a function and can look somewhat messed up if complex regexp's are written.
If you start with small examples, you will get used to both, I bet, usually it takes it's time though like with all things
You can do a lot of tasks with sed as you can do with awk. The easy thing with awk is, that it is by default designed to parse fields and has therefore variables like NF, FS, OFS, .. and some more and is very readable compared to sed.

So here a short list, when what to use (other people might use the tools with other priorities) basically:

grep --- search every line of a file for some content
egrep/grep -E --- for using regular expressions
sed --- substituting, filtering, line and multiline parsing, ...
awk --- parsing fields, lines and multiline parsing, substitution, ...

For your wc -l problem, maybe try something like this for examle (asuming your commented lines start with a hash (#):

Code:

root@isau02:/data/tmp/testfeld> cat infile
line of code 1
line of code 2
# comment 1
line of code 3
line of code 4
# comment 2
line of code 5
root@isau02:/data/tmp/testfeld> for file in `find . -type f -name "infile*" -print`; do echo $file `grep -cv ^# $file`; done
./infile 5

Edit: Ie. you have to go into the use of other regular expressions for comments in c/c++ like those /* ... */ and don't forget to escape them with usually backslashes.