I recommend equal temperament, in particular with Suszki:
- When you learn to play in more and more keys it will be easier because they will sound and "feel" more similar to the keys you are playing in as a beginner. If you use just temperament you will get overly attached to Keys like G, D, and A major because the violin will be more resonant due to sympathetic vibrations.
- It will be harder to play in tune with a piano and/or ensemble.
Use the Tuner to Train you Ear to Equal Temperament
Every day, try tune your strings by hear from the an A440 generated by the app. Then see if you got the A to match. If you didn't correct it. Then tune the other strings by ear by listening for relative fifths (Tune E from A, tune D from A, tune G from D). Then use the tuner to see if you were off (using equal temperament).
When in an ensemble (or orchestra) you will generally tune your as a group to A440, which corresponding to violin's second highest string, the A string. From that, by ear, you then proceed to tune your other strings relative to that A (unless you happen to have absolute pitch, which I will choose to mostly ignore for this post).
Understanding the difference
If you use tempered fifths (equal temperament), you end up with the following tuning:
G3=196Hz, D4=293.7Hz, A4=440Hz, E5=659.3Hz
If you use perfect fifths, you will end up with the following tuning:
G3=195.55Hz, D4=293.33Hz, A4=440Hz, E5=660Hz
Your G and D string will be flat and your E string will be sharp in just tuning (from a equal temperament perspective). This will be more noticeable in certain keys (when you are start to learn stuff with more sharps and flats).
What about fiddle music?
Ya will use a lot of double stops, open strings, and harmonics. You will also often play in those keys that the violin likes (G, D, A for example). So just tuning is probably right for this, in particular when playing alone. However, I'm sticking to my guns and recommending equal temperament for the reasons mentioned. When you are ready for a lot of real fiddle playing, you can tune those nice open fifths, but learn Suziki with the equal temperament.
Whatever you do, understand the difference, tune by ear and verify with the tuner (not the other way around), and have fun!
When working on your intonation while playing (not tuning the instrument), I would focus less on the tuning system and instead focus on consistency. This means that regardless of what tuning system your note actually is, make sure that the note stays the same throughout a section or passage. When the same note changes in pitch and isn't consistent, this usually what most makes something sound out of tune. There can be subtitles to this with different keys when not using equal temperament, so when learning using equal temperament will help you with the most important aspect of good intonation - consistency.