1. Total Annihiliation

2. Starcraft

3. Command and Conquer : Red Alert 2

I'd say neither, and wait for UT3.

In BF2, you'll often be facing n00bs that will TK you for various reasons, such as AMGUTOOKMIPLANE, or GIMMEHMACHOPPA. Also, be prepared to have a short life. Often you'll eat bombs or artillery shells shortly after spawning, or die to spawn camping tanks / snipers, or die to some fool with a C4 loaded vehicle.

UT2k4's Single player is the best part IMO. The AI is decent, there's a bunch of mutators, no hackers, and a ton of difficulty settings. However, if you join online games, you'll often faces very skilled players that will make short work of you, or n00bs spawn killing at your base with a manta.

I spent more than 30 hours online on both games and those are my observations.

Check out information on http://www.bizarreonline.net/ or the steam website here : http://storefront.steampowered.com/v/index.php?area=news&id=1085&s=0,22,305&i=0,300,320,240&cc=CA&skin=3&client=1

Hardest ? I'd have to say F-Zero GX. Story missions are super tough on normal, imagine what it's like on Hard and Very Hard modes.

Worst ? Hum. I don't remember it's name, but it's a card / summoning / fighting game for the GameCube.