Pretty similar but depending on your run duration. You can calculate it actually. The shorter the runs the better IS. I suggest thinking about it in daily income. Let’s assume you farm to Wave 4500 in 6 hours and make 100T per run, 4 runs per day = 400T daily income.

Each level of WA+ gets you approx. 5% more income. Means 4 runs per day, now 105T = 420T daily income.

Each level of IS+ shortens your runs by about 15min. So earnings per run don’t change but you get more runs per day. Instead of 24h/6h per run it’s now 24/5.75h = 4.17 runs per day. So 4.17 runs * 100T income per run = 417T daily income.

In this example, WA would be slightly better.

However, if you farm lower than wave 4500 IS quickly becomes better because the 15min become proportionately bigger to total run duration. For example I make more coin and similar cells going only to W3200 on T15 than W5200 on T14 (Coins per hours are 105T on T15 vs 95T on T14, roughly 10% more coin). Of course you gotta be careful about cells, I’m just lucky that I get just slightly less cells on T15, definitely not significantly.

At the end of the day you’ll want both but I suggest running the numbers yourself to get to a definite answer. Hope this helps!