As someone who grew up using Apples and was around when the SE/30, etc, were new, the IIx and IIcx seemed more impressive to me than the SE/30 was. Yeah, the SE/30 was/is the most powerful original-style compact Mac, but the II series was more capable. Then, when the IIci came out, that seemed even better.
Of the '030 PDS Macs, the SE/30 is more capable, with respect to memory, etc. Add an accelerator and a 32-bit clean ROM, and it'll blow the case lid off the IIsi. The one nice thing about the IIsi is that the M1212 14" Macintosh Color Display's stand seems designed for it. Fits the case lid perfectly, whereas, on a IIci, it's a little too wide and curved, of course. I've personally chosen the IIci as my '030 Mac... No, it's not as fast as a IIfx, but it takes up less space, while being better than both a IIsi or an SE/30.
IIci pros over IIsi:
25 MHz
8 memory slots
68882 FPU on the logic board
runs 6.0.4 and 6.0.5, in addition to 6.0.6, 6.0.7, and 6.0.8, plus all the 7.x variants
two ADB ports
three Nubus slots - add a sound card, if audio input is important
Cache card slot
normal speaker connection
More powerful power supply available from the 3-slot metal case Macs, like the Centris/Quadra 650, etc.