Alright, well for starters, there aren’t many 1.3 servers out, so whatever is there...just take it- or make your own server.
You can categorise lag into 2 sections-
FPS Lag and Latency Lag [ Or wtvr ].
FPS Lag is caused by the amount of RAM other programs are using whilst your playing.
Whenever I want to start playing ESF, I always have to close this Adobephotoshopcs program because it eats around about 70MB of RAM.
latency Lag is simply caused by other programs digging through your net. Examples are...
MSN, Downloading, Torrents, Prown, all that stuff.
In order to get into a server which will guarantee you a good play, search for the list...and look at the latency line. Its a line with lots of numbers. Go into the server with the lowest integer. Hope that helped.
-GuZzie