It depends on what extra options you want.
Teac 3300 SR is a classic older model, can have severe head wear and gummed up pinch-roller linkage, is it in good condition ?
Some has different speed, could be 7-1/2 and 15, or 3-3/4 and 7-1/2.
Also a few 2-tracks can be found compare to 4-track.
Both models were sold so be sure to check that part.
Teac 6300 I really like, taller and more dependable model, not many options but very nice sounding machine. Same thing, check headwear before buying.
4-track, 2 channel stereo and auto-reverse. Speed: 3-3/4 and 7-1/2.
Teac 3340 S, is a 4-track multi track machine with sync funtion for laying track after track in sync. A studio recorder, but can be used for "normal " use if you want.
Speed: 7-1/2 and 15. Early to mid 70's model.
Check head wear and if all 4 channels is working correctly.
Many times these has a broken pc-board behind the head-cover for switching between the channels... a bump on the switch and goodbye pc-board.. a new board cost $ 130.00 + labor.
Teac X-1000 R is the newest one with more bells and whistles like auto-reverse, recording both ways, built in DBX function, digital counter, return to zero function, pitch control and more, but prices are higher then all the other 3 models you mentioned.
A gentleman contacted me yesterday wanted to sell a non-functional X-1000 R for $ 500.00 + shipping, notice Ebay with high prices for this model, but be careful as many times they don't work correctly on arrival.
Of course the best part is to find a non touched, low hour deck, then a good chunk of money is a good idea.