whats a better strategy when neither team has a jungler... push really hard then fall back and farm the side jungle creeps while your minions are at their tower to deny them gold, or just try to only last hit and zone/harass to deny xp?

I would say take advantage and push hard, just keep on a close eye on bottom lane. Also if your having trouble with top lane you can always go bot for a gank.

Ye, pushing hard and farming top then as well works quite nicely. a good tactic for sure.

A good champ to take top could be one that goes over walls. Tryn, Corli etc. Allows for better ganking over the wall behind dragon, into top lane. (when the enemy has pushed it) Also its good to have someone quite mobile if you are jungling.

I push really hard and then gank bot.

I agree with the general consensus of pushing hard. Assuming someone has clairvoyance or you're keeping the mid jungle warded (which you should always be doing on TT), pushing top hard gives you a lot of map control. This allows you to own the mid jungle, and gank or at least harass bot often; and as long as you're keeping eyes on the jungle, it's pretty easy to not get ganked yourself.