Depends on your warlord. Inspiring warlords have really good access to encounter heals, maybe better than a cleric (haven't compared the two post Martial/Divine power) and excel at granting saves. They don't heal as much damage overall, but it's easier to make one with a good number of encounter triggers. Also their encounter healing powers tend to have better non-healing aspects, especially damage.
Tactical warlords excel at granting attacks and bonuses.
Either one will generally deal good damage, better than most healing-focused clerics. A strength cleric can close most of the difference, but they would do it by dedicating feats and powers to damage rather than healing, and end up about in the same spot.
In fact I believe warlords are still near the top as far as damage dealing leaders, though I haven't really done a careful comparison since the PHB came out.
Also, don't just compare them to clerics. If anything clerics are like fighters, clearly one of the favorites and very possibly overpowered, particularly if you just look at healing.