The following is an overview & not exhaustive by any means.
Pro's: One stop plug 'n play. 22 amp models, good effects, 8 patch memory, VFS5 gives patch changing,effect on/off, reverb on/off. Easy to use on stage. Portable, great ‘vintage’ tone, 66 factory presets, global reverb.
Cons: No FX loop, floor control limited (no stomp mode), FX selection combinations are limited, no MIDI or USB, no switchable cabinet models. VT30 has no extn cab out. Extn cab out on VT50 disconnects internal speaker, 8 patch memory too limited for some, no patch naming facilities, no wah/exp pedal in VFS5, no channel LED's in VFS5, factory settings cannot be permanently changed/modified in any way, no inbuilt tuner. Volume is limited to the amp rating you choose, unless you mike up through the PA.
Pro's: Beautifully compact & light, 33 amp models, 50 user programs & 50 factory pre-sets, 4 mode EQ for amp/PA compatibility, USB connection, 11 pedal effects in addition to 'normal' effect options, Tuner, assignable expression pedal built in (wah, volume, expression) 11 switchable cabinet models. Great for computer recording, has edit software, very versatile. Many good factory pre-sets that sound great straight out of the box. Expression pedal can kick in any of the 11 pedals including distortions.
Cons: some buttons & operation are fiddly, needs amp/PA to play live, harder to tweak live on stage (more complex than VT, so takes more tweaking, & its on the floor - bending down vs tweaking controls of an amp positioned higher). Less plug 'n play than a VT (A 'trap' of all MFX units is that sometimes you can end up spending more time tweaking than playing!). No foot control of FX on/off (other than Expression pedal), tuner/bypass mode awkward to engage with feet, no fast scroll through patches with feet which is a nuisance, as foot buttons only go up/down one patch each time you press.
Tone depends on how unit set and what you're playing through (amp, PA etc), so again a little less 'plug 'n play'. Tone is dependent on skill of setting patches - can sound great, but takes more time to get used to. In the right hands, can be awesome!
Recording, use through computer, creating patch libraries, playing through PA, portability, versatility, bells & whistles - The TLLE wins
Plug 'n play, quick set-up, simplicity, easier to tweak on the fly at gigs, more conventional and simpler amp controls, tonal consistency (speaker is
inside!), - The VT wins
Different animals for different needs – so depends on exactly what you want!
From what appears on the forums, the TL's appear to have very few problems, whereas the Valvetronix amps get more forum time (this is partly, but not solely, because more amps than TL’s are sold). Both have their quirks - TL's can have issues with software & expression pedal squeaking etc, VT's can have issues of software, dirty jack sockets and dry solder joints. All amps run hotter and have speakers on board, so you'd expect less to go wrong in an MFX unit. Similar considerations apply comparing any amp with any MFX, so this is not just a Vox thing.
Easier to change the valve in TL & you can get some tonal variation with different valves in the TL's. Interestingly, this has little or no effect in the VT's.
Ain't choice a bitch?LOL So, why not enjoy the best of both worlds & get both, if you can!
BUT a word of caution – I don’t recommend you use them together - a modelling MFX unit and a modelling amp don't mix! Amp models will conflict, you'll get extra noise, & you'll be miserable!
UPDATE: You can turn the amp models off on the TLST ! (per patch, but not global). So you CAN just use it as an effects pedal with a Valvetronix if you wanted to!
The VT30 is great, & the 10" speaker gives a nice vintage tone. It's loud enough for rehearsals and small gigs, but if you need more volume, there's the VT50. The VT15 is great for home, but the VT30 sounds better, & is more flexible with more clean headroom & volume.
I’ve been playing the ST through my Laney VC30-210, and it’s just AWESOME & great fun! I love it - I would definitely want one in addition to my amps, but not in place of them.