^this (as been said earlier)I'll go another route and not recommend a particular brand but rather advise that you think about any ergonomic preferences you have and then find basses that might fit that. With a 6'er, coming from a 4, there are two main measurements that may or may not be important to you:
scale length (4s are typically 34", 6'ers are usually either 34" or 35")
bridge spacing (4s are typically 19mm give or take, 6'ers can be anywhere from 20mm down to 14mm)
Beyond that, details like nut width and width at the body joint can have an impact. Some people have no issue with going from very different measurements, others find it problematic. It took me about five tries to figure out what I wanted/needed in a 6'er. For instance the Ibanez SR basses have fairly tight bridge spacing - some love it, I didn't.
If you've done a lot of experimentation with different instruments you may already have some preferences. Of course with practice you likely can make anything work, but depends on a lot of factors. In my case I end up switching between 4 and 6 in a set, and for me having the same scale length and bridge spacing made that easier. But what works for me may not work for you. 6 is a different beast than 4, and I found I needed to approach it differently and adapt some of my technique. Ymmv.
I have a Yamaha TRB6II, 35" with a great B which I attribute (maybe wrongly) to the scale length. Note : 35" is a significant difference with 34" and depending on your finger length and technique it can cause strain. I'm not too eager to try a 36" Tune model ! The MTD Z6 also is 35". You may want to have a look at the Andrew Gouché Kingston model.
Ibanez SR models are 34" and have a tight string spacing and I'm not too keen on that. The Ibanez BTB series are 35", and have a wider string spacing although not as wide as a TRB6 (18mm) or a TRB6JP (19 mm). BTBs are tempting but IMO lack character until you reach the range where they have brand pickups and electronics and by then they get more expensive and the competition.
A less expensive alternative is the Cort Artisan A6.
To sum up : I love my TRB6II, no wonder Yamaha have been selling it for 20+ years (now they sell it as TRB1006, made in Indonesia. Everyone agrees that the used japanese made TRB6II are a better deal). TRB6JP2 may be found for less than 2k used, but 19 mm makes the neck really wide for my taste.
MTD Kingston KZ6 and AG model : I'd buy one of these if I hadn't already had the Yamaha.
Ibanez : extensive catalog but I always feel they're like "Jack of all trades but master of none"
Cort Artisan A6 : top of the line from a very capable company, I'd consider this model if I was looking for a 6er.