100 amp service wire size from transformer to meter/panel
Voltage drop may be an issue, at this distance.
The Canadian Rule (don't permit more than 3% voltage drop at 80% of breaker trip, which is the max provisionable) requires a wire size &quot;bump&quot; around the 175' mark on distance.  This is not required in the United States, but it's a viable rule of thumb.   Under the Canadian Rule

for 100A breaker (80A computed) #1 will come in at 2.99% drop.
for 200A breaker (160A computed) #4/0 will come in at 2.88% drop.

And that's fine, because those are your minimum wire sizes anyway.
Wires carrying your whole service get a 17% discount
When you have wires carrying your entire service, you get to compute your mandatory wire sizes off 83% of service size.   So this leads us to #2Al for 100A, and #4/0Al for 200A.
A feeder wire never needs to be bigger than the service wire by this rule.
However, since you are seriously contemplating a 200A heavy-up, I do not recommend laying #2 because you'd only need to upgrade it later.
All other feeders need to calculate on full-boat
If a feeder doesn't benefit from the above exception, then it must calculate full-boat ampacity.  For the wire types offered in aluminum, that is
100A = #1 Al ...... 200A = 250 kcmil Al.
A 2-RV stands needs less than 100A.
The RV provisioning rules allow a &quot;discount&quot; for feeder size when the feeder serves multiple RV stands.  The discount means #2 aluminum wire (rated full-boat 90A) is acceptable to feed two 50A RV stands.
Run wires ONCE
The reason I'm arming you with all this data is because I want you to not have to replace wires later.  Run the wire you need and don't look back.
&quot;But my 100A meter won't take 4/0 wire!&quot;  That's OK -- get three Polaris connectors rated for 4/0.  Use those to pigtail down to #2 or #1 Al wire to land on the meter lugs.  Of course those Polaris couplers are about $20 a pop, so figure that into the cost.
On panels - think BIG
What's important with panels is the number of breaker spaces.  Spaces are dirt cheap, so never allow a future situation where  you want to add a circuit or feeder but can't because the panel is full.  Honestly, &quot;help, my panel is full&quot; is our #1 panel question here.  Just get ridiculous numbers of spaces.
Typically, 100A panels have only a few spaces... most panels of respectable size (24-space and larger) are 200A bussed.  If they are main-breaker, they typically have 200A main breakers.
That is fine -- you can go ahead and use it anyway.  If it is downstream of another breaker, then the local breaker doesn't matter - it's only there to be a disconnect switch.   E.G. if you use a 100A &quot;meter-main&quot; you can run to a 200A-main-breaker panel and that's fine - the 200A breaker serves merely as a disconnect so its size doesn't matter.
If this panel needs a 100A breaker, then you have 3 choices:

Buy a 200A main-breaker panel and swap out the main breaker for 100A
Buy a 200A main-breaker panel, disregard the 200A main, and install a 100A breaker in a normal breaker space and backfeed it, as the main. Label it as the main breaker.
Buy a 200A/225A convertible, main-lug panel, and buy a retrofit main breaker that is 100A.