Renectly, R4i Gold 3DS RTS is very hotly on the market, because it support NTRBoot. It means you can use R4i Gold 3DS RTS and a magnet to install boot9strap to hack your New 3DS/3DS/2DS XL.
Except R4i Gold 3DS RTS, there also have some other flashcart support NTRBoot, see below.
Acekard 2i HW-44
Acekard 2i HW-81
R4i Gold 3DS (RTS, revisions A5/A6/A7) (r4ids.cn)
R4i Ultra (r4ultra.com)
R4i Gold 3DS Starter (r4ids.cn)
R4 3D Revolution (r4idsn.com)
Infinity 3 R4i (r4infinity.com)
DSTT (some flash chips only!)
But some of these have stopped production (Acekard 2i), and some are expensive (R4i Gold 3DS Starter), the best choice is R4i Gold 3DS RTS.
R4i Gold 3DS RTS is only $18.5 USD at digimartz.com. This is an reliable official reseller, you can rest assured to buy.
Here i’d like to inform you in advance that the price maybe rise a lillte after this month, if you have interested, just buy now!