Welcome to the boards!
The first thing is to understand that against the most often encountered prey, the SM/CSM, Gaunts
aren't supposed to inflict casualties... If they do, that's a bonus. The real reason for taking Gaunts against these enemies is that once they get into CC with them, the CC now blocks LOS to a majority of models which means that the rest of the Tyranids will get to move closer without getting shot as much. The real killers are the slow and fragile Genestealers, fast and fragile Raveners or the Warriors with a variety of options for speed and weapons.
Yes, TMCs are amongst the real killers of the Tyranids swarm, but a CC of normal-sized models won't be blocking LOS to them.
I myself field two types of Gaunts in regular games:
Leaping Gaunts of some description, usually Gaunt + Leap + AdrG I + ScyTal. I try to have at least 2 broods of these, with a minimum of 14 Gaunts per brood, and one Hive Node Mutant per brood to help keep them in check if they're outside Synapse.
Spinegaunts (Gaunt + SFist) for cheap mass... Though against some opponents they can be very nasty! Dark Eldar Wyches, for example, dislike these rather heavily!
In Seeding Swarm lists I go with Toxinspinegaunts (Gaunt + ToxSac + SFist), since they will most often be arriving via Deep Strike and thus can be of more immediate use than CC Gaunts. They're also still relatively cheap to field in large numbers, while having a useful Str to deal with lighter vehicle Rear armour without the support of nastier creatures.
Instead of Spinegaunts, some take Scythegaunts (Gaunt + ScyTal)... Slightly more expensive than Spinegaunts, but more effective in CC where they're supposed to end up in. However, the problem with these is that You won't get enough ScyTal per Gaunt box to equip both walkers and leapers with them. This leaves one with few options:
- Use Spinefists for base, add a blade-like protrusion with Greenstuff, Milliput or similar epoxy putty.
- Build ScyTal from scratch using the aforementioned epoxy putty.
If You intend to field both leaping and walking Gaunts in Your army, this is only way I can think of to acquire more ScyTal.
Alternatively, You could use the ScyTal for the walkers, and bit-order Gargoyle Wings to convert Your leaping Gaunt bodies into Gargoyles.