I rarely say anything directly. I am pretty loud when it comes to keeping my own teams spirits up, and this can vary between genuine encouragement to ripping my own team mates to shreds to keep everyone else laughing and bouncing.
I aim general comments at the entire oppo loud enough for most to hear if necessary. Example being a recent game, we had our clubs beer festival on at the time which i used to put together a nice little narrative about the way the oppo were batting.
They won the toss and batted on an absolute road of a deck. Runs were easy to come by you just had to bat time and get bat on ball. They were all taking huge heaves from ball one, honestly not even having a look at their first ball or a new bowlers first ball. It was like a conveyor belt with batsmen coming and going. I started to announce that there must be one hell of a beer festival back at their club, and that our beer festival obviously isn't good enough etc.
'Our ales are good ales guys, I promise.'
'The way these chaps are batting this beer festival they need to get back to must be special, i might need to get myself a ticket'
'road. win toss. bat. badly. lose. back home. beer festival. good day out chaps'
etc, various variations on the theme. It was mainly to keep our guys laughing but it was curious to see not one of the oppo decided to prove me wrong and bat sensibly. They finished about 150 shy of a par score and we knocked it off easily.
I fully expect return fire from any comment i make, be it general or aimed at a player directly. When i strode out to open the batting a couple of them made everyone aware that i was very chatty when they batted, so i best have a world class cover drive. I of course got a duck and trudged back to the pavilion with a hefty send off.
The personal nonsense can go a bit far and sometimes i deem it way too aggressive with lots of personal insults and swearing. It all goes over my head and i usually respond with silence, a nod or as an early attempt to put it to bed - 'why don't you say that to someone who gives a *$!* mate?'
I've seen minor counties players get stuck in to young lads batting at 9 and 10 with the game all but over, i have no idea why someone who plays at such a level deems it necessary to behave like that especially when everyone can see the game will be done in a matter of balls.
Theres the other side of the coin of course. You get batsmen who want to be chatty, some who even seem like they want to instigate a bit of back and forth, i tend to blank them completely in an attempt to throw them a curve ball, as GarretJ mentioned, it can put some players off.