There is a difference that I perceive quite often (not always), in that liberal social action tends to come with few strings attached, the emphasis being on plain help. Evangelicals more often use their works as a sort of vehicle for proselytisation, and this, I think can get in the way of the good things they do and can pervert the compassionate motivations they have.

This would certainly be the is that the work is primary and any form of proselytisation (which is probably the wrong word in the first place) is largely a distant secondary or even tertiary issue.  I make my comments about proselytisation because many governments use it wrongly.  It has a very specific meaning which has been lost in recent years: it refers to promising physical or economic benefit in return for conversion, and is frowned on by the majority of Christians, evangelical or otherwise.  It is not synonymous with evangelism.