They seem similar, but they are indeed very different. If you are used to playing a blapper, the PB might fit your playstyle although you may find that you are trading in some of your damage potential for safety in the form of heals and shields.
The WS on the other hand is a little bit more mezz-heavy in human form and has some awesome self-buff potential in the form of Dwarf Mire, Sunless Mire and Eclipse which turns the Nova form into a very sturdy juggernaut of pure destruction (I call it the PFFoD - The Purple Flying Fortress of Doom).
All in all the PB is a little bit more self-reliant and may be easier adjusted for solo-play, but in teams he just can´t hold a candle to the damage output of a tri-form-WS after reaching a certain level.
So, which one you are going to be happier with depends on your personal preferences.
If it has eyes, you can blind it, if it has blood, you can make it bleed, if it has a mouth, you can make it scream.
well i have heard (like you say) that PB are a little more like blasters, and more solo happy, where as WS are more like trollers. I think that i would be happier with a WS to be honest, cause it is different to what i have been doing, but in all honesty i really don't know, i was looking for some difference, which you have given me.
Differences mostly in powers, and how you have to play them, it seems you have more buffs and troller like powers as a WS, am i right in thinking that?
way i think about it is a Pb starts of better then a WS (more damage better res) but a WS has powers that lets it be a lot better then a Pb for a period of time, basically Pb is more simple then a WS.
Hmmm, I have read posts before claiming that PB are similar to blasters and WS are like controllers. I can´t say that I agree too much, although some of a WS´s powers are controllerish. (Actually I see it is quite difficult to explain them within a few sentences as versatility is the main reason for their epicness.)
In my eyes PBs are more like blappers only with added self heals and shields while WSs have more similarity to a nifty kind of corruptor with a hold and an immob thrown in for good measure (together with a little bit of dark armour).
Other differences I might add are that PBs are quite self-reliant and that there is not too much sinergy between their forms (dull pain carries over and makes the dwarf form quite durable and the nova form a little bit less squishy) while the WS needs crowds of (living or dead) enemies to shine and has great sinergies between his forms (black dwarf mire, sunless mire and eclipse turn the nova into a thing of pure beauty)... oh, and the WS pets are so much cooler than those stupid, stupid, stupid photon seekers. 
So, if you are used to a blaster´s firepower and want to play something with similar damage potential but different playstyle you might be a little bit disappointed by the PB. The WS on the other hand might seem a little bit weaker in the early game, but from the 30ies you will be able to make your teammates want to have a WS, too. I just love my Purple Flying Fortress of Doom. 
If it has eyes, you can blind it, if it has blood, you can make it bleed, if it has a mouth, you can make it scream.
Peacebringers are good, they get the good powers at first, then the Warshardes manage to put the perfecter meter at higher levels.
My suggestion is to start a Peacebringer, then if you get bored, build a Warshade.
PBs don't get the ability to properly SLOT all their powers till later on tho.
And you won't have access to both Dawn Strike and Photon Seekers until 35, then Light form's at 38.
Both kheldians fully mature around the level 40 mark. (Slotted Light form and Slotted Eclipse)
PBs are generally better against single targets, WS are generally better against groups. PBs can buff themselves anytime at will, WS can buff themselves much more but need to get very close to large mobs in order to do it.
yeah.. warshades are pretty darned dull until the 30's.. even double mire doesnt shine until you get eclipse.
as soon as the 30's hit though... whoa... pet, then quasar (THE best looking power in the game, and with double mire outdamages BU + Dawn Strike by miles), then eclipse - and your path to being epic is complete. I never realised what it felt to be 'epic' until i got eclipse. with a good sized mob you can stand toe to toe with the psi-clock king in nova form, without taking a dent...until it wears out at least... then you kinda go 'splat', but it's okay cause you can then self rez and go into dwarf form for a bit =D
if you want something you can go to PvP with.. pick a PB. warshades need dead bodies for a load of their powers.. something which you dont often find in PvP because they always bugger off and respawn before you've managed to fire off your pet.
on a side note.. have you ever been in an arena match with travel powers turned off and tried to use nova form? lol it just bounces slowly along the floor...
i have a level 44 blaster, and hope to have him at 50 my the end of the month, this is my first 50, and was wondering what the differences between WS and PB are? which one am i going to be happier playing with