What's the difference between these motherboards?

Main differences among the boards are: 1) Power Phases, 2) Debug/Diagnostic LEDs, 3) SATA port layout, 4) M.2 slot quantity and heatsink/cover, 5) PCIe x16 slot reinforcement, 6) Wireless connectivity, 7) LAN port quantity, 8) Video output ports, 9) USB 3.1/3.0 internal header speed, 10) Fan header quantity, and 11) Shrouds/cover.

Below is a specs comparison table. Those marked with Red are "worst/unfavorable specs", those marked with Blue are "best/favorable specs", the rest that are unmarked have "equal or have insignificant difference" when compared among the 3 mobos in question:

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║ ║B║ POWER |MOS| 2- ║ RAM ║SATA3║M.2[KEY-M]║ PCI-E 3.0 x16 |ADD'L║PCI| ║W|RJ45@REAR║VIDEO H║ AUDIO SP|J║BUTTONS║P║ USB @ REAR U║HEADERS @ MIDBOARD|RGB LED║ARMOR║SIZE║PCB &║
║ BRAND / ║I╟-----┬---┤FET|DIGIT║Q┌---╫-----╫------┬---╢Q┌---┬-----------┬---┴-┐GPU║-E |P║I├---------╢ |V|D|D║ @REAR |D|A║ @REAR ║S╟---┬---┬---┐S║USB|USB|USB| |FAN/| STRIP ║ @ ║Ht.x║ACCNT║
║ MODEL ║O║PHASE|ATX|HT.|DEBUG║T|RE-║(Qty.║ QTY. |HT.║T|RE-|Max. Speeds|Multi|12V║3.0|C║F| LAN ║D|G|V|M╟-------┤I|C║CL FLSH║/║TOT|3.1|3.0|B║3.1|3.0|2.0|T|PUMP|HEADERS║I/O &║Wdth║+ LED║REF.
║ ║S║(VCC)|12V|SNK| CODE║Y|INF║@90°)║3.0 x4|SNK║Y|INF| | GPU |PWR║ x1|I║I|CNTROLLER║P|A|I|I║ CODEC |F|K║CMOS BK║2║QTY|C|A|C|A|2║ C |19p|9-p|B|4pin|12v|+5v║AUDIO║(mm)║COLOR║LINKS:
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║Gigabyte ║ ║ 7 | | | X* ║ | ║ 6 ║ | ║ | |x16/-/x4, |2wSLI| ║ | ║ | ║ | | | ║ | | ║ | ║ ║ | | | | | ║1**| | | | | | 2*║ ║ ATX║BK/GY║Gigabyte Z370 Aorus Ultra Gaming
║Z370 Aorus ║2║(4+3)|1x8|ALL|*LEDs║4|YES║(4/6)║ 2x | X ║3|2/3|x8/x8/x4 | or | - ║ 3 |-║-|1x I219V ║-|-|1|1║ALC1220|1|5║ - | - ║1║ 8x|1|1|0|4|2║**v| 1 | 2 |Y| 6x | 2 |5V/║ I/O ║305x║ + ║WEBSITE
║Ultra Gaming ║ ║ | | | only║ | ║ ║ | ║ | | |3w-CF| ║ | ║ | ║ | | | ║ | | ║ | ║ ║ | | | | | ║3.0| | | | | |12V║ only║ 244║ RGB ║MANUAL (12ME-Z37AULG-1002R, 2017/09/25)
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║Gigabyte ║ ║ 9? | | | ║ | ║ 6 ║ | ║ | |x16/-/x4, |2wSLI| ║ | ║ | ║ | | | ║ | | ║ | ║ ║ | | | | | ║1**| | | | | | 2*║ ║ ATX║ BK/ ║Gigabyte Z370 Aorus Gaming 5
║Z370 Aorus ║2║(TBD)|1x8|ALL| YES ║4|YES║(ALL)║ 3x | X ║3|2/3|x8/x8/x4 | or | - ║ 3 |-║Y|1x I219V ║1|-|-|1║ALC1220|1|5║ - | - ║1║ 8x|1|1|0|4|2║**v| 1 | 2 |Y| 8x | 2 |5V/║ YES ║305x║Lt.GY║WEBSITE
║Gaming 5 ║ ║ | | | ║ | ║ ║ | ║ | | |3w-CF| ║ | ║ | ║ | | | ║ | | ║ | ║ ║ | | | | | ║3.0| | | | | |12V║ ║ 244║+ RGB║MANUAL (12ME-Z37ARG5-1001R, 2017/09/25)
╠══════════════╬═╬═════╪═══╪═══╪═════╬═╪═══╬═════╬══════╪═══╬═╪═══╪═══════════╪═════╪═══╬═══╪═╬═╪═════════╬═╪═╪═╪═╬═══════╪═╪═╬═══╪═══╬═╬═══╪═╪═╪═╪═╪═╬═══╪═══╪═══╪═╪════╪═══╪═══╬═════╬════╬═════╣
║Gigabyte ║ ║ 10 | | | ║ | ║ 6 ║ | ║ | |x16/-/x4, |2wSLI| ║ | ║ |1x E2500 ║ | | | ║ | | ║ @ | ║ ║ | | | | | ║ | | | | | | 2*║ ║ ATX║ BK/ ║Gigabyte Z370 Aorus Gaming 7
║Z370 Aorus ║2║(4+4 |1x8|ALL| YES ║4|YES║(ALL)║ 3x |1/2║3|ALL|x8/x8/x4 | or | - ║ 3 |-║Y|1x I219V ║1|-|-|1║ALC1220|1|5║Ins| - ║1║ 7x|1|1|0|5|0║ 1 | 1 | 2 |Y| 8x | 2 |5V/║ YES ║305x║Md.GY║WEBSITE
║Gaming 7 ║ ║ +2) | | | ║ | ║ ║ | ║ | | |3w-CF| ║ | ║ | ║ | | | ║ | | ║ide| ║ ║ | | | | | ║ | | | | | |12V║ ║ 244║+ RGB║MANUAL (12ME-Z37ARG7-1002R, 2017/09/25)
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Generally, based on features, the Gaming 7 is considered as an "Extreme/Enthusiast" model, the Gaming 5 is a "High-End" model, while the Ultra Gaming is a "Mid-Level/Mainstream" model.

For more info on other models, you may want to check this: http://www.tomshardware.com/forum/id-3529650/z370-motherboards-lga1151v2-comparison-tables.html