I am using now non eth and I need to repair them once a cow run - with eth titans I would have to wait to replenish or they replenish faster?

I can't answer your question, but I use Lightning Strike mainly so eth Titan's has no problems.

I recommend Lightning Strike especially in cows

They don’t replenish faster. It just seems that way. Because when you repair, you are starting from max quantity. Thus it takes longer to almost run through them

Thuderstroke best!!

maybe you kill faster with eth titans so you don't throw as many

This has been tested and proven. Eth titans replenish at about 1.5 times slower than non-eth titans.
This is countered by having 2 sets of eth titans.
Suggestion would be to only use your charges for large packs (should only need about 2-3 throws if you have most of your gear) then clean up with CS or drag the cows to the next pack.

OR as mentioned before buy yourself another set!

Lightning Strike is super, especially in cows and Chaos.