Here are two different roles a warden often chooses
1. The melee warden Secondary healer/Secondary tank
With AAs, he converts his spells to melee attacks. These do more damage and auto-upgrade as you level instead of buying new ones. These are very nice. Also, he would go down the STR line, giving him some very handy abilities (like chance to group heal per hit, and a high chance of double attacking per hit). In the Warden EoF tree, you have the combat art conversion abilities. At the end of it, you can choose an ability that causes you to crit on 75% of your melee attacks. This mean's some SERIOUS damage output (especially if you get the other melee attacks in other druid lines). Also, the warden would use the Warden EoF mitigation bonus (maxed out, it increases your SELF mitigation buff effect by 50%). With the extra druid AA points, he normally maxes out melee attacks from other lines.
Completely false, melee Warden can be and is just as good as being main healer.
IN GENERAL: He is a pretty good healer, but not as good as he could be since he's using tank stat gear and not WIS stuff. He makes an AWESOME solo player and secondary "tank" (I was able to take on ^^^ heroic even con mobs without dying all within melee range). Unfortunatly, he has a lower mana pool.
Misleading, melee Wardens usually have 2 sets of gear 1 for solo/grouping and 1 for raiding and hard instances. So we are great at both worlds.
2. The healer/caster warden Primary healer, support
This warden generally maxes out the AGIL/STA/INT lines the best he can. He also goes down the movement line in the Warden EoF tree. He can't taken much beating, but he has maximized his healing ability, along with giving him good DPS in the INT line. Not as good DPS as a melee warden...but he's a lot better at heals...which is what is expected of a warden in higher end tiers. Sure, you cannot solo as good in tight areas with no room to root/nuke things, but you can make your GROUP survive longer and get into places you couldn't as a solo player. You can also solo better (not quicker!) than a melee warden if there's a lot of room to move around (root/nuke). However, if there's little room, a melee warden would be the best.
Extremely misleading a Warden going down the agi line vs str line does not heal for anymore, if anyone he uses more mana from overcasting on fast ticking hots, I have yet to see any raid encounters where faster hots are required. Faster hots just tick faster they do not heal for more, although a str Warden can and will in some situations actually heal for more.
In general...I'd say a solo player would definetly want melee warden...and a groupie player would want the healer/caster warden.
With the caster Warden casts times are much longer than with the melee Warden, a melee specced warden can do more damage and spend less time casting ca's, in fact cast times are so fast on CA's the normaly a melee warden can get off all CA's between heal casts. and have the advantage of healing entire group with boon proc.