The Avanti RtlExplore is better ! I use it to check my RTL code , it show some messages that help me to solve the FPGA synthesis issues (FPGA synthesis tools give some clueless error message) !
have a look at Atrenta Spyglass and you will agree nothing can beat it in lint..it has more comphrensive rule checks than any other lint tool and it also checks against certain standard like STARC , OpenMore, xilinx, Design Reuse (RMM) etc...
In HAL custom rule can be coded. It provides standard VPI ( Verilog procedural interface ), VHPI ( VHDL procedural interface ) , CPI ( common front-end procedural interce) and HAL API , which is tool's own C programming application specific interface .
I would imagine Spyglass to be better (and have heard so as well) - after all it is one of their bread winners for Atrenta, I strongly believe that if it is your bread winner, you would try and be the best in the industry. Leda I use it almost daily, does the job..