Scale wise, I am not sure which would be better...1/60th is nice, big and can be expensive....1/72 is nice as it would go nicely with existing mecha (Robotech, Gundam etc) and as such it wouldn't be to difficult to mod those into Battletech varients or such...not to mention you can get aircraft in this scale also, so making Aerospace fighters from existing airplanes would be readily doable. 1/35 scale would be interesting as well as it would work out nicely with military models in production. The cost would be down somewhat as there would be less of it needed. 1/48...well...that'd be HUGE! 1/144 scale......borderline tiny....not much bigger than what we have now in pewter.
That's my 2cents...... Personally, 1/72 has the most benefits.
The advantages of 1/72 is that you can get relatively cheap 1/72 Baindai Destroid kits ($20 a piece for the Archer and the Rifleman), the Wave Destroid kits are a bit more expensive ($65 a piece for the Rifleman and the Warhammer). And best of all, the 1/100 Bandai Officer Pod Glaug (Marauder) will probably work with them. The 1/72 Valkery kits might be a little big for Phoenix Hawks/Wasp/etc. (maybe 1/100 will work), the real problem comes from the Dougram mechs, a lot of the 1/48 kits work with 1/60 BT, and not with 1/72 (they become taller then a Warhammer). 1/72 is better for the older 25mm Battletroops Kurita/Steiner platoons (individually still produced by IWM) and the 25mm Clan Elemental (RPE). Getting other 25mm miniatures is not easy, probably best to look at GZG. No ebay Mad Cat, Vulture and Atlas (or the selection of 1/60 fan made resin models).
1/60 Has the advantage of the older Mad Cat, Vulture and Atlas (or the selection of 1/60 fan made) resin models. The IWM 30mm Clan Elemental and the legions of 28-32mm ish miniatures and Vehicles available. The 1/60 Yamoto Destroids, the 1/72 Glaug kit (ebay => Expensive), the 1/48 Dougrams, etc. And if there are any future large scale developments I suspect that they will also be in the 1/60 and 30mm range (and not 1/72). So if you want to go really big scale this is your best bet.
1/144 fall in the 'N-scale' range that is really popular with a small (but very vocal) subsection of BT fans, this scale actually ranges from 1/120 to 1/160 and build around the Mechwarrior plastic Range. Keep in mind that 1/144 is actually twice as tall as most of the BT tin Mechs. There's also a large selection of resin fan build Mechs in this 'scale'. There are also a lot of Macross/Dougram toys that work very well in this scale so most of your Unseen needs are met (although some of these kits are somewhat difficult to come by and can now relatively expensive). There's actually one 1/144 sci-fi miniature maker that I know of and that is dp9 with their Heavy Gear, Reaper made some 'N-scale' vehicles and infantry, but it seems that they are phasing those out.
I'm also taking a look at 1/100 - 15mm scale, there's a huge range of 15mm (more like 18mm to the top of the head) of sci-fi miniature manufacturers making infantry, vehicles and terrain. My large collection of 1/87 Rafm Heavy Gear Models are actually closer to 1/100 and with some of the awesome 15mm infantry/vehicles made by the likes of GZG/Micropanzer/CMG/Rebel Minis/Khurasan/etc I saw some great opportunities. I recently came across some cheap 1/100 Destroid kits, so I'm curious how that'll look (Warhammer ~12.5cm tall).
For general BT gaming 6mm gaming has the largest range of models, after that it's the n-scale range. If you want large mechs 1/60 has the largest range, but can be a lot more expensive. If your only interest lies in the Unseen Macross Mechs, 1/72 is very acceptable, if not, 1/60 is your best bet.