The differences are feature set and form factor. Sound quality is identical in all of them.
The instrument units have cable modeling to simulate the effect (losses) that a guitar cable adds to your signal chain. The G50 is obviously a pedal board receiver and the G90 has a A/B switch to easily switch between transmitters if you use more than one instrument/transmitter.
The XD-V has a 1/2 rack form and an environment filter for reduction of unwanted sound. You'd have to try that with an instrument to see if you'd like that or not.
Thanks for the quick reply.
If I understand the cable modelling on the the G50/90, that is most useful if you switch back and forth from wireless to wired and don't want to change any settings yet have your guitar sound "exactly" the same. If you're never going to switch, I can't see wanting to model in a fake cable?
Maybe it's the sound engineer in me and not coming from the player side. My son wants the wireless on his bass guitar. I will get the best thing - just also want the most flexible unit and don't want to lock into just a guitar wireless system.
I have used other manufacturer standard wireless/beltpack combos for mic'ing guitars in the past and I don't ever remember someone complaining about any changes in signal quality between wireless or cabled.
The only thing I see with the XD-V70 is that I'll need the mini-XLR to 1/4" cable for pickup versus the G50/90 where the beltpack takes a standard 1/4". That little bit of cable is the least of my problem I think - just wanted to make sure I wasn't missing something important before deciding which to purchase.
The TA4 (what you refer to as mini XLR) to 1/4 inch also provides a different impedance for the guitar or bass than a regular mic sees (its wired slightly differently in the connector). So that should give you a head start on bass or guitar appropriate matching. Liking or not liking the sound of cable modeling is a personal choice and sometimesthe particular requirements of the performance.
"The only thing I see with the XD-V70 is that I'll need the mini-XLR to 1/4" cable for pickup versus the G50/90 where the beltpack takes a standard 1/4"."
No ... G50/90 and V70L all use TA4f connections to the transmitter. The G30 and V30 use 1/4"
So I bought the XD-V70L and the guitar cord from the Line6 store. Everything came today, easy to setup and my son took off to practice. I'll find out later how he likes it but I couldn't have got anything easier!!! Thanks for the helpful and quick answers everyone. I'm very happy I purchased the XD-V70 rather than the G50 for the extra flexibility and use.