You're going to get a plethora of personal preferences so don't hope for a consensus of opinion here.
Most Shimano kit is compatible, so you can mix & match without too much risk, but if you're upgrading you'll get better results with a matched set. Yep, sounds like a contradiction I know, but trying to match new with old does carry with it a certain amount of the unknown.
If the budget can afford it, the 2008 model Deore XT Shadow rear derailleur in medium cage is a nice piece of equipment and goes well with RapidFire shift levers.
The new front derailleurs come in top-swing, conventional, or E-type configurations to mount on almost any frame and the adaptable clamp means one size fits all. Also the multi-pull mechanism takes top or bottom-pull cables, so again can be expected to suit any bike.
Life is too short to bother with idiots