The M16 or SV3 brass is very nice and can be used in all 3 modes; it's heavy - tarnish would be the only "issue".
If you need to use it in 18350 this would be the next best.
Mix and match? You can buy both a brass SV3 and the Alu/Brass SV3 - you can have the Brass tube, Brass endcaps and lighter and more tarnish resistant aluminum outer sleeves. Or buy the Alu/Brass Sv3 and a full brass m16 (for the m16 brass inner tube - if you don't like the knurling on the SV3 inner tube) and swap sleeves and topcaps.
Note: the M16 aluminum/brass parts are not interchangeable with the full brass m16 or the sv3. So don't get the alu/brass m16 unless you want to just keep it that way.
A few people are scared of; or have been dealing with stripped aluminum 510 connectors (top caps)
The newest model PV2 (steel/brass/copper) is probably the best of all materials (and looks imo) - except that it can't be used in 18350.
You don't have to decide; just buy them all like I did
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