well altough i might not be the one to ask
i'm pretty good at aggressive inline skating.
what that is basically, well it consists of tricks like jumps, grinds, and so on. it requires a certain tipe of skates.
3 mayor ones to mention: (there are a lot more variations then these)
Aggressive-tipe skates: ( notice the groove in the middle.. meant for grinding , aka jumping on surfaces and sliding on an edge/pipe anything you can fit it in.)

Fitness-tipe skates: (unlike the other this one has a little "break" in the back so you can slow down without any fancy footwork, heavier then the aggressives)

Speed-tipe skates: (very large wheels, there are models with a full boot that hold your foot better, but a lot them are like this)

there are also hockey-tipe skates, sth in between speed and fitness, models with 4 wheels, speed models with 5 wheels, we have aggressive models that have a 2 wheel & anti-rocker setup, or simple 2 wheel with a v shaped frame ( mook frames ftw!) and so on.
for a beginner i think its good to start with fitness skates.. of course i'm oriented to the opposite side then T-rex apparently
and i only rode with speed skates like 3-4 times in my life.
the bigger wheels make for much quicker trip, for some people i know it got a bit harry with the turns.
aggressives have a solid core wheel 60 mm or below in size , and they have a flat profile to offer better grip, room and to get you closer to the ground for more control, but they sacrifice speed (which of course an aggressive skater doesn't even need)
you can turn on a dime with them but if your planing on going for long "runs" then aggressives will be hard to deal with.
speed wheels are generally 90mm and above (some models have under 90) and as the name suggest they are SPEED! but not so easy to control
the profile is narrow and elliptical so a "sharp edge" so it also has less friction
fitness and hockey wheels are in between.. generally in the 70-80 zone, with the elliptical shape, they offer a good mix of speed and control.

fitness skates are a good general all rounder and i think they are one of the best choices to start out with.
but i've had people start with aggressives, and they worked out well, but the price tag on those is significantly higher then the fitness skates, and are a lot harder to find ( can't even buy'em in my country)
and fitness skates will be readily available, better suited for the city then speed skates. and better suited for a good few hours of skating (when you're actually going somewhere!) then aggressives
besides wheel profiles you have the durometer, which basically is the hardness of the wheel
this image can explain how that works:

that really doesn't affect you much, if you have smooth roads ahead of you then a harder wheel is ok, if its a bit bumpy then with a harder one it can get a little annoying ( also the smaller the wheels the worse that gets

)
really this doesn't matter for a recreational skater. it will only make a very slight difference. but i thought i'd mention it anyway.
now there's also the bearings that are in the wheels .. you will hear ABEC - now that is just a rating of the bearings the higher the rating the more precise the bearing and the "smoother".
now that doesn't mean that you go out and get the highest one you can find .. like ABEC9 or above.
ABEC1 is the lowest.. the " crappy" kind they resist a long while but they aren't very smooth or fast but they are CHEAP!
actually the ABEC rating is more about precision and smoothness then speed... and even more about PRICE TAG..
and the system WAS NOT designed with inline skating in mind. but for machines that need to be very precise.
and for a recreational skater (or even a semi-pro) the difference between ABEC 5 to ABEC 7 isn't important at all.
most skates you come-by will have from 3 to 7 .. speed skates go up to 9 and some over.
what i'm actually getting at is that if you see a skate that has ABEC10 labelled on it and they say well its the best quality and ask for 100$ more for it then the ABEC 7 then better off going for the abec 7 instead.
i agree that K2 skates are good, there are some good 80mm wheeled fitness models with K2 .. i used 3 skates from K2 one of them fitness the other two aggressive, and didn't have any problems with them, and their price is very good compared to some other equal quality skates .. My opinion is their good starter skates.
NOW
in terms of protection, i was never a fan of any guards, especially the knee guards because they really annoyed me, couldn't find a helmet O_o , but i liket the wrist/hand guards , the elbow guards i didn't take..
but hey i was skating since i was like 5-6 years old. Got my first inline skate at age 8, but got my first set of guards at around age 10 xD
one thing is to check them out before you buy and make sure their not uncomfortable, especially knee guards, i have found them to be very unpleasant if they are to tight or made in a weird fashion that cuts into the back of your knee , it needs to be comfortable if your going on those longer runs.
it shouldn't be very tight, walk around (or better skate around a bit) and see if it bothers you.
ohh and i'll just mention this, when buying skates, try'em out ad move around in them a bit, some skates are just designed WRONG, and have parts that will screw up your foot after a few hours,
i had a pair of fitness skates that made my feet bleed and i couldn't walk properly because some idiot decided to put a little metal rivet right at the ankle.
if you feel it pushes in on a spot anywhere on your feet then better off looking at alternatives.
also i got asked a few times if someone should buy their shoe size .. or a bit bigger.. well that really depends on the company and the model and the shape of your foot xD
if its to big then your foot can move around, you have to tighten it more then normal, and that can cause pressure points sometimes that might hurt your foot.
but if they are an exact tight fit that can also cause problems (although most skates i used have good room for your toes..)
K2 as i noticed generally have a good fit and hold your feet well, and all 3 K2's i had were slightly larger sizes then my shoe size and thats how they felt comfortable for me and didn't have many problems with them.
my current
Xsjado skates go around this problem completely by having a footwrap (shoe) and its damn stylish if i may say so.

The good thing about these is that you can use any shoe you want, just step in the boot and you're off. my favorite skate of all time.
ok i'm already going off topic, and i wrote WAAY too much.
sorry for the block'o'text but i hope it was of some use to you.