Just my demo project demonstrating differences between serialization sizes of JSON versus protobuf, both uncompressed and compressed with deflate.
My own conclusions really boil down to processing time versus space. Space is negligibly different. From the data below, compressing JSON versus compressing protobuf isn't that different, so I'd make a decision on which to use based on processing time.
I bet that JSON processing will be flying with the new .NET Core 3.0 JSON API, but obviously I don't really know until I actually test.
1624 25b90d78-3b94-4356-a72c-265d4dea6eaf.100.compressed.dat
1705 25b90d78-3b94-4356-a72c-265d4dea6eaf.100.compressed.json
2318 25b90d78-3b94-4356-a72c-265d4dea6eaf.100.dat
6619 25b90d78-3b94-4356-a72c-265d4dea6eaf.100.json
214 38af6f2a-9426-4642-aa1f-2a91a61e0555.10.compressed.dat
251 38af6f2a-9426-4642-aa1f-2a91a61e0555.10.compressed.json
236 38af6f2a-9426-4642-aa1f-2a91a61e0555.10.dat
667 38af6f2a-9426-4642-aa1f-2a91a61e0555.10.json
127359416 8aa39f6e-d7c5-4edb-a9a5-04a2b821d7e7.10000000.compressed.dat
142347211 8aa39f6e-d7c5-4edb-a9a5-04a2b821d7e7.10000000.compressed.json
230879578 8aa39f6e-d7c5-4edb-a9a5-04a2b821d7e7.10000000.dat
660898029 8aa39f6e-d7c5-4edb-a9a5-04a2b821d7e7.10000000.json
12736743 b6f3fe46-44bd-48d8-8209-f69682e54a13.1000000.compressed.dat
14235987 b6f3fe46-44bd-48d8-8209-f69682e54a13.1000000.compressed.json
23086826 b6f3fe46-44bd-48d8-8209-f69682e54a13.1000000.dat
66088812 b6f3fe46-44bd-48d8-8209-f69682e54a13.1000000.json
1275057 c36e6fa7-3b05-4f5a-b473-114c93db447a.100000.compressed.dat
1423686 c36e6fa7-3b05-4f5a-b473-114c93db447a.100000.compressed.json
2308654 c36e6fa7-3b05-4f5a-b473-114c93db447a.100000.dat
6608815 c36e6fa7-3b05-4f5a-b473-114c93db447a.100000.json
14201 c3bc602a-57de-4abd-8e5b-2b8c049ad712.1000.compressed.dat
15012 c3bc602a-57de-4abd-8e5b-2b8c049ad712.1000.compressed.json
23116 c3bc602a-57de-4abd-8e5b-2b8c049ad712.1000.dat
66127 c3bc602a-57de-4abd-8e5b-2b8c049ad712.1000.json
129069 ff66951e-a96a-4ed0-92c9-b7695f3a0230.10000.compressed.dat
143091 ff66951e-a96a-4ed0-92c9-b7695f3a0230.10000.compressed.json
231089 ff66951e-a96a-4ed0-92c9-b7695f3a0230.10000.dat
661115 ff66951e-a96a-4ed0-92c9-b7695f3a0230.10000.json