As of right now, there's really no point in flashing anything on the Nexus 4. Now, if you want T9/Smart dialer (dial number or letters and the contact will automatically pop up)m you'll have to wait for AOKP/CyanogenMod or the likes.
Personally, if I'm going stock/vanilla Android, I'll stick with Google's stock for max battery life and stability.
Now, if you want to try something awesome, then go with MIUI (which I would assume will be released for the N4 once it becomes more widely available). MIUI is probably my favourite ROM of all time as it mixes stock android with iOS (and makes it look better than both combined). MIUI is going to be previewed in a week or two, so look out for that.
http://miuiandroid.com/community/ to keep up