While both champions (ch/r & ch/p) are great tanks, the play style is completely different.
You notice this mostly when clearing mobs.
Any mob or boss you hit with rune pulse is instant aggro (with high damage hammer), but rune pulse has cast time and a small cooldown which make it not always useable when needed...
ch/r has a few xtra ranged attacks and the 50% xtra patt, aggroing runaway mobs is easy (mobs have lower pdef values)
Combined with Shadowstab it can do a lot of damage.
ch/r is awesome when your raid is not that strong
When a ch/r is geared for dps (str/patt) he can do some awesome damage while tanking a boss
ch/p with some healing gear (healing points) has in light pulse an awesome aoe that does damage and heals nearby party members, which also gives healing aggro!
Besides of that, the damage buff, cleansing, healing, immune, etc. what a ch/p can do is really awesome!
If the raid is strong, then a ch/p shines!
But clearing mobs with a ch/p is slower compared to a ch/r or a k/m, but it does help if your healer is a d/wd and has placed his briar shield on you.., then you can probably solo a lot!
cheap statting would be 1 sta/patt dawn, the rest str/sta, maybe a 2th sta/patt if you have trouble find the stats
If you dont want to do dps (with str/patt stats), then level up shieldform.
With a ch/p with al of those extra stamina bonusses you'll have a xtreme high hp & pdef and when needed a high mdef