Personal preference but although xr 30s are great ,I prefer the xr 15s for placement . As you have the ability to move them where you need them . It’s hard to split the xr 30 unless you have a good table saw lol kidding but you get the idea . If your tank is deep as well you have the ability to stager xr 15s . I run mine in a hanging fixture with t5s in front and back and my xr 15s staggered where my tank needs them in between .