As an Avid macross collector I can help you out I hope.
Old bandai Valks and the reissue ones are 1/55
New er Yamatos are either 1/48 or 1/60...
There are 2 versions of the 1/60. The old one was a parts former, which may not bother you, but I had to through it out there.
The new 1/60 s are based ofrf of what they learned with the totally awesome 1/48s. They are perfect transfomrming.
You need to look for a VF-1S with super parts (often it is called a super/strike part) Super parts are jetfire's armor, Strike parts are jetfire armor with a big honkin cannon. Most of Yamoto's packs have parts for both. Yamato puts out a Hikaru VF-1S that is very close to the jetfire color (red and black stipe is reversed) But the super parts will need to be painted as they only come in light blue/gray.
Unless you want to get really nuts and buy a red Miria valk, but thats a whole 'nother investment

Bandai (and KO companies) put out the old jetfire VF-1s mold all the time, and its great for a vintage reissue, but it's going to have limited articulation and such, and will go with your G1 collection, not your MP collection.
Toynami is generally considered crap as far as quality and line art accuracy by most Macross collectors. YMMV
As far as which would go with the seekers, well there is the rub.
1/48s are about as tall as MP prime and megs. 1/60s are a bit smaller than MP seekers...a little taller than a classics jetfire really.
the 1/55 s are closer in size to Mp seekers, but they really are not going to blend very well, especially if your seekers are in dynamic poses.
Yamatos are expensive, but are MP quality Items. I have 5 1/48 Vf-1 yammies, and 2 1/60 yammies, have had no complaints about them at all.
I also have 2 old jetfires, and I love him for what he is, but he is strictly on my G1 self.
Hope this helps. You can also check out the forums at macrossworld, though lots of topics there involve the newer Macross frontier series (Vf-25s and Vf-27s are the shiznit:P)
Warning! Buying a 1/48 Yamato may open up a whole new world of toys to waste money on... lol
Oh and price... VF-1S yamato will run from 100-250 US each maybe a little more depending on scale, and Super parts. Yamato sells vlaks with and without the Super parts, and super parts seperately. It is not always cheaper to buy a combo pack, sometimes you can find super parts pretty cheap by themselves.
As far as toynami valks and bandai reissue vlaks... I really don't know because I have never bought them. I know you can get a cheap KO of the mold for less than 20 bucks, but it is a KO with Ko quality.
Bottom line Jetfire was a VF-1S with Super Parts. (there are VF-1J, Vf-1A, etc so make sure its VF-1S) 1/55 is the old bandai version, 1/60 and 148 are the newer Yamato versions.